Transcript Training Presentation

Knowledge for Children
Low Aim is a Crime, but not high ambition
–NCERT ‘Guidance in Schools’
A need for every Child
Today at Kayalpatnam
1
CFCs damage Ozone Layer ?
 Chloroflurocarbons (CFC) used by refrigrants, coolants, cleaning
agents, etc are main eaters of ozone present in atmosphere.
 Highly unstable, an ozone molecule readily splits when hit by
ultravoilet radation. Energy of life-damaging UV rays is thus
converted into harmless heat and never reaches the earth. This
process generates Oxygen atom and Oxygen molecule, which in an
ongoing cycle, recombine to form new ozone molecules.
 When CFCs go upward to stratosphere and get struck by ultra violet
rays, it releases chlorine atom, which attacks an ozone molecule,
pulls away one of the three oxygen and forms a chlorine monoxide
molecule thus destroying the ozone molecule.
 Oxygen atoms from the new chlorine monoxide molecule is pulled
away by free oxygen atoms freeing the chlorine atom to restart the
cycle.
Guidance for Children
2
Dust – Appear & Reappear
 Dust is mostly tiny fragments abraded from large things.
 Dust knows no borders.
 Dust cloth may simply stir up dust.
 Charged particles of dust are attracted to surfaces with
the opposite charge.
 An antistatic spray may help by providing a very thin
layer of insulation between the opposite charges.
Guidance for Children
3
Age of Fossils
 Atoms of same element having same atomic number but
different mass number are called isotopes.
 Radio active isotope of carbon is 146C which has a half life
period of 5730 years. Half life period of a radio active substance
is defined as the time required for half of its atoms to
disintegrate.
 The radio isotope of carbon is continuously produced in the
atmosphere by the action of cosmic rays on atmospheric
hydrogen.
 Plants and animals absorbs 146C with natural carbon 126C. In
living beings, the ratio of 146C/126C is a constant when a plant
or animal dies the 146C disintegrates without being replaced.
Hence by determining the ratio 146C/126C in fossil the age is
determined. This method is called “Carbon dating”.
Guidance for Children
4
Height of Mountains Measured
 The method used is known as “Triangulation”.
 If one knows one side and two angles of any triangle (or two sides
and one angle), one can find out the rest of its measurement.
 One side of the triangle is usually a level piece of ground between
two landmarks.
 The third landmark is the apex of the triangle. The angle it makes
with each of the first line is measured.
 Instrument for measuring these angle is called a transit. The transit
works vertically which is called levelling as there is a spirit level at
the base of the instrument that indicates when it is in level. By
raising the sight to any landmark or a mountain, the same process
of measuring angles can be done and the length of one side (the
height) can be measured.
Guidance for Children
5
Lava is hot ?
 Magma is predominantly a molten silicate saturated
with gases that are dissolved in it.
 Due to high pressure existing in deeper part of the earth
where volatile compounds are in a dissolved state.
within magma, diminishing its viscosity and increasing
the degree of its mobility and chemical activity.
 Volcanism unites all the processes connected with the
outflow on the earth surface.
 Liquid products of volcanic eruptions are represented by
lava.
Guidance for Children
6
Black and White Clothes
 Black material radiates heat faster than white material,
and similarly absorbs infrared heat faster.
 Although it is true that dark objects radiates heat more
effectively than light-coloured ones, the amount of heat
radiated from a body is proportional to its absolute
temperate raised to the power of 4.
 In Summer, it would be better to wear white as the
benefit of black clothes radiating heat away quickly
would not outweigh the disadvantage of them absorbing
infrared heat more quickly.
Guidance for Children
7
Rainfall – Measure ?
 A simple rain gauge which any one can use to measure rain at
his place consists of a funnel (3 to 4 inches in diameter) fitted
into a bottle (about 1 litre capacity) to collect the rain water
and a measuring cylinder.
 An air-vent is to be provided to prevent accumulation of rain
water in the funnel in case of heavy down pours.
 Rain gauge is kept on the ground without obstructions.
 If the area of opening of the funnel is 80cm2 then for 1cm of
rainfall the volume of water would be 80cm2 x 1cm that is
80cm3.
 If the total volume of rain water (in cm3) collected, over a
specified period, is divided by 8, we get the rainfall in mm in
that place over the given period.
Guidance for Children
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Smell after Rain
 Smell immediately after a shower is due to certain
volatile chemical compounds released by a group of
soil-inhibiting bacteria called streptomycetes.
 Streptomycetes are abandant in dry warm soil, a million
of them can be detected in a gram of soil.
 They release compounds such as geosmin and 2 methyl
isoborneol when wetted by rain water after a long dry
spell.
 Thus we get the odour only after the first rain of the
rainy season. The smell can be felt in newly ploughed
lands also.
Guidance for Children
9
Rainbow Formation
 When the Sun shines after a shower, we often see an arc
of beautiful colours in that part of the sky opposite to
the Sun.
 This is due to reflection and refraction of the Sun’s rays
as they fall on drops of rain. As a ray passes into a drop
of rain, the water acts as a tiny prism. The ray is bent,
or refracted as it enters the drop and is separated into
different colours. As it strikes the inner surface of the
drop it is further refracted and dispersed.
Guidance for Children
10
Mountain Tops are Cooler & not hot?
 Air is a poor absorber of sunlight.
 Sun heats the Earth which is a better absorber, and the
Earth then heats the air close to it.
 Hot air rises because it is less dense than surrounding
cooler air at the same pressure.
 As it rises, a mass of hot air expands because the
ambient pressure is less. This expansion cools the air, so
the temperature of a thermal bubble decreases with
increasing altitude until it reaches an equilibrium.
 If you climb 40Km above the Earth’s surface, you would
find that it gets much warmer.
Guidance for Children
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Sound in Thunder
 Warm, wet air surges upwards into the sky and cools dramatically
forming thunderstorms.
 Some of the water inside the clouds freeze and strong air currents
make the ice and water droplets bump together.
 This knocks tiny charged particles called electrons from the ice and
so there is a build-up of electric charge. This charge is released by
a stroke of lightning. The lightning heats the air around it to an
incredible 30,000C.
 We hear lightning first and then thunder because light travels faster
than sound.
 By counting the seconds between the lightning and thunder and
dividing by three we get the distance to the storm in Kilometres.
Guidance for Children
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Finger Cool Faster
 Our body is like a container of heat.
 The amount of heat per unit volume (say, every cubic
centimetre) of the body is approximately the same.
 But the fingers and nose have a greater surface area per
cubic centimetre than other parts of the body and so
they cool down faster.
 As soon as heat is delivered to the fingers it escapes
through the surface. But the rest of the body does it
slower and so are a little hotter than the fingers.
Guidance for Children
13
Coconut Oil Freeze in Winter
 Oils are liquid fats. Fats are esters of carboxylic acids which are
either saturated (do not contain double bond) or unsaturated
(contain one or two double bond). These esters are derived from a
single alcohol called glycerol and are glycerides.
 Fats with greater percentage of unsaturation tend to be in liquid
state and fats with greater percentage of saturation tend to be in
solid state at room temperature.
 Coconut oil contains nearly 91 per cent of saturated fatty acids.
Still, it is liquid at room temperature because of the presence of
more number of short chain (C12 and C14).
 Because of the greater percentage of saturation, coconut oil can be
solidified at low temperature and becomes solid during winter
when the temperature falls below 20 degree centigrade.
Guidance for Children
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Water in Mud Pot remains cool
 Mud pots contain many minute pores through which
water can slowly ooze out.
 These pores increase the surface area of water and
consequently increase evaporation.
 For water to evaporate it requires some energy while it
takes as heat from the water itself.
 This results in lowering the temperature of the water in
the pot.
 Water never becomes ice because the system is not a
closed system and so it can take up heat from its
surroundings.
Guidance for Children
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Drops are Spherical ?
 Liquid drops tend to be in a state of minimum surface
energy which is directly related to the surface area.
 The force, surface tension, which is trying to hold the
droplet together, therefore tries to reduce the surface
area of the drop.
 Mathematically only a sphere has the smallest surface
area for a given volume, compared to other geometric
shapes.
Guidance for Children
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Sunflower facing Sun
 Due to Phototropism.
 Phototropism is a growth-mediated response of a plant
to simulation by visible light. The response is stimulated
by a hormone called auxin present in the stem.
 Auxins promote lengthwise growth of plants.
Guidance for Children
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Lotus leaf does not get wet
 Lotus leaf does not get wet due to outlayers of cells in the
epidermal layer of leaves.
 They contain cellulose, which get converted by cutin by the
process of cutinization and form an impermeable membrane on
the cell wall known as cuticule.
 Cuticle, is a layer of wax-like substances which are simple lipids
containing one molecule of fatty acids esterified with one
molecule of long chain alcohols instead of glycerol.
 A molecule of wax consists of odd number of carbon atoms
ranging from C25 to C35. These are highly insoluble in water &
chemically inert because these do not have double bonds in
their hydrocarbon chains. Hence waxes from a protective
covering.
Guidance for Children
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Lemon drops create white spots?
 Lime juice contains 6 – 10 per cent of citric acid.
 Cement is a complex mixture of calcium silicates and
calcium aluminates.
 When drops of lime juice fall on the floor, a chemical
change takes place.
 One of the products is calcium citrate which gives a
white colour on these spots.
Guidance for Children
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Cut Apple turns Brown
 Apple contains an enzyme known as polyphenol oxidase
(it is a copper containing enzyme).
 When the fruit is cut, this enzyme becomes reactive as
it comes into contact with air. It reacts with the sugar
present in the fruit and results in the formation of
brown colour on the cut surface.
 If cut apple is dipped in an ascorbic acid solution
browning of the cut surface can be prevented as the
acid inhibits activity of the enzyme.
Guidance for Children
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Temperature affect ripening bananas
 Temperature changes can delay or hasten the ripening of
banana.
 Banana is a tropical fruit; adapted to ripen quickly at a
certain stage of its development and at a particular
temperature and humidity. It continues to ripen after
harvest, with more and more of its starch converted into
sugars by the action of enzymes.
 When harvested, a banana contains about 20 percent starch
and only 1 percent sugar. By the time the fruit is ripe, the
proportions are reversed.
 Banana releases comparatively large quantities of ethylene
gas to help itself ripen; the gas will even ripen other fruit put
in a bag with a ripening banana.
Guidance for Children
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Mango ripens in rice tin
 During ripening, a number of enzyme-assisted reactions take place
inside the fruits. The list includes softening of tissues, hydrolysis,
changes in pigmentation, flavour and respiration rate, and
conversion of carbohydrates and organic acids into fruit sugars.
These changes are induced by ethylene which is also called a
ripening hormone.
 It has been found that during ripening, ethylene production goes
up. An ethylene-forming mechanism and breaking of the
insensitiveness to ethylene are attained only when fruits reach a
certain physiological age.
 When unripe fruits are kept inside a sack or tin of rice, the time
needed to attain this critical physiological age is shortened. It could
be that the fruit to totally cut off from light which promotes
yellowing. The ethylene produced in the fruit also diffuses rapidly
through the fruit’s tissues.
Guidance for Children
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Plants survive without leaves
 Abscission is a physiological process whereby plants
shed a part, such as leaf, flower or fruit.
 This is promoted by a plant hormone called abscisin
produced by leaves and fruits.
 Extreme temperatures limit the metabolic activities
such as respiration, of plants. Such a reduction,
consequently necessitates only a low level of
photosynthetic activity.
 Less Energy required could be got from photosynthetic
activity of a few green cells, present in the terminal
regions, after all the leaves fell.
Guidance for Children
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Red parts in Sugarcane
 Red portions in the stem of cane is due to a fungal
disease called red-rot caused by the organism
Glomerella tucumanensis. The organism attacks during
the conidial stage (imperfect stage).
 When the affected canes are split open, the tissues of
the internode which are normally white or yellow-white
will become red in one or more internodes usually near
the base.
Guidance for Children
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Trees Reduce Air Pollution
 Trees act as sink for carbon dioxide. Through
photosynthesis they synthesize carbohydrate using
Carbon Dioxide, water and sunlight.
 Trees release oxygen, which is needed by other living
organisms.
 They act as barriers or curtains for dust through the
settlement on the dense foliage of trees.
Guidance for Children
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Visibility in the dark
 Vertebrates have two types of photosensitive cells, rods and
cones, so called because of their shape.
 The rods, which are long and fat, contain large amounts of
visual pigment and they mediate vision under dim
illumination (scotopic vision).
 The cone cells, which are relatively small, mediate daylight
vision (photopic vision) and colour sensation.
 In nocturnal animals, the retina is mainly made of rod cells.
 Rhodopsin, a photosensitive pigment, present in rods is
decolourised by photons (light particles) and slowly
regenerated in the dark. This ensures better vision for them
in dim light.
Guidance for Children
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Eyes glow in dark
 Birds’ syrinx (the functional equivalent of our larynx or
voice box) is much simpler than that of humans.
 Some birds with more rudimentary syrinx can become
more proficient in creating sound.
 In birds, the syrinx is located at the bottom of the
trachea. Sound is produced at the syrinx as air flows and
the volume is controlled by muscles in the trachea. The
sounds are then emitted with little or no modulation.
 Human vocalisations originate from the larynx at the
top of the trachea. The larynx is more complex and
produces relatively simple sounds.
Guidance for Children
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Eagles fly with flat wings
 Eagles adopt an energy-saving flight mode called gliding. Their
broad wings and broad rounded tail enable them to exploit
thermals in the air.
 Thermals are upward air currents in the atmosphere caused by the
absorption of heat, from the sun or load, by the air.
 The birds flap their wings slowly and laboriously in the air in wide
circles, but once they catch the rising air they begin to soar
effortlessly without even a single beat up to a point where the
warm air has cooled and stopped rising.
 From this point, they start gliding down to another thermal, which
they spot by seeing other groups of rising raptors or perhaps by
their delicate sensitivity to even minute changes in air currents.
 Their primary feathers are spread out to obtain the maximum
advantage from the rising air.
Guidance for Children
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Blinking Of Eyes
 Blinking keeps the front of eyeball clean.
 Blinking is done by means of muscles in the eye lids and
the cleansing by tears.
 The tears are secreted in a little gland and carried
along to the eye and when our eyelids open and close
the tears are poured over the front of eye and they
wash away any particles of dust or any other harmful
substances.
Guidance for Children
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Run before Jumping
 Due to Newton’s law of motion: All objects living and
non-living, have inertia – a tendency to remain in its
present condition.
 If a body is at rest, it will have a tendency to remain at
rest in future also. In the same way, if a body is moving,
it will have a tendency to continue its movement at a
later time.
 If we stand at a point and jump, we will not be able to
cover a good distance because our body will try to
remain standing (be at rest), and we will have to spend
a lot of energy (or more power) to jump long distances.
 Thus, we run before jumping before saving.
Guidance for Children
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Bees Find Their Way
 Information about the source of food is informed to others during
round dance or waggle dance.
 Round dance is going in small circles, clockwise or anticlockwise,
alternately.
 Waggle dance is tracing a figure of eight.
 Round dance is used if the food is of short distance [say 100m].
Waggle dance is used if the food is far away.
 They use round dance or waggle dance to find their way.
Alternatively, they can return to the hive by remembering the
angles of triangles formed by the position of the hive, the sun and
bee though this may vary with time.
 Bees can also perceive polarisation of sunlight and thus use the sun
as a compass.
Guidance for Children
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Ants find their way to hidden sweets
 Antennae, the two hair-like structures on the head of
the ants, help them in locating sweets.
 These chemoreceptors help them to perceive smell and
taste through minute sensilla, or sensory cells.
 If sweets are wrapped in paper bags or any other
wrappers having minute holes, the odour carried by the
air will be sensed by the sensilla.
 If the antenna are removed, ants cannot identify the
smell and distinguish them from other foods.
Guidance for Children
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Ants don’t get hurt when they fall
 Fall of a body is controlled by gravitational attraction of
the Earth.
 Heavier object is attracted more than a lighter object.
 This attractive force is opposed by an upward thrust
(resistance) offered by air on the body. This resistance
also depends on the surface area of the object. That is,
if the surface area is more, the resistance is also more.
 In the case of an ant, the force of gravity is almost
balanced by air resistance and so it is able to land
safely.
Guidance for Children
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Ants go in a line
 Once an ant find an abundant source of food, it returns to the
nest with a sample of food. While returning to the nest, it
presses its abdomen to the ground and at frequent intervals
extrudes its sting, the tip of which is drawn lightly over the
ground surface, much like a pen drawing a thin line.
 As sting touches the surface, a volatile chemical (trail
pheromone), flows out of a gland (Dufour’s gland), associated
with the sting. In this way, the ant draws an invisible chemical
line from the source of food to the nest.
 Since the chemical is highly volatile, the trail remains only for a
short time. Hence, all ants constantly draw the line over and
over again.
Guidance for Children
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Houseflies increase in Summer
 A single female may lay eggs 4 to 6 times and each time
each female lays 120 to 160 eggs. They lay their eggs in
clusters on compost, waste heaps, manure and dumps.
 The condition required for laying eggs are moisture and
favourable temperature. The eggs hatch in 8 to 24 hours
depending on the temperature.
 The whitish larvae moult twice to become the familiar
white maggots in 7 days.
 The maggots transform into quiescent reddish brown
pupa from which the adult flies emerge after 5 days if
the temperature is optimal. Summer provides all the
favourable conditions.
Guidance for Children
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Bulges when mosquito bites
 Bulging is mainly due to histamine.
 It is widely distributed in the tissues, the richest source being
the mast cells that are normally present in the corrective
tissues adjacent to the blood vessels.
 Preformed histamine is present in mast cell granules and is
released by mast cell degranulation process which in response
to the stimulus caused due to irritation at the site of the bite.
 This histamine causes dilation of the arterioles and increases
vascular permeability venules. This in turn causes venular
endothelial contraction and widening of the interendothelial
cell junctions, where the extra vascular fluid accumulates
causing inflammation.
Guidance for Children
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Do Snakes Hear ?
 Snakes are deaf.
 Snakes actually respond to vibrations produced on the
ground and not to the sound waves produced by the
mahudi [Snake Charmer], in the air.
 Snakes do not have ears, instead they have a long bony
road called columella auris that extends from fenestra
ovalis to the quadrate bone. It is this bone which helps
the snake to detect the vibrations.
 It is to be noted that the charmer first hit the ground
with the pipe before playing it.
Guidance for Children
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Spiders don’t get caught in their web
 Spiders secrete an oil on its legs that prevent it from sticking to
their own web.
 Silk, made up of proteins, secreted by the silk glands, are made
into fibres as thin as a thousandth of a millimetre.
 The proteins are water soluble when secreted, but when made into
a fibre, some physical and chemical changes take place, and so,
after a while the fibre becomes tough and does not dissolve in
water.
 Spider at first makes the radials from the centre and then the
spiralling threads. There may be 10-60 turns in a web. To capture
an insect, spider places a small glue droplets throughout, except at
the place where it rests.
 The vibrations of the captured insect are sensed by the spider.
Guidance for Children
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Blood Clotting
 Blood has the ability to clot or coagulate, when it is
withdrawn from the body.
 In the blood vessels, the blood remains in a fluid
condition: shortly after being withdrawn, it becomes
viscid and gelatinous and sets into a firm, jelly-like
mass.
 Clot consists almost entirely of red corpuscles entangled
in a network of fine fibrils or threads, composed of a
substance called fibrin. It also contains platelets and
plasma.
 Certain substances promote coagulation (procoagulants)
and others inhibit coagulation (anticoagulants).
Guidance for Children
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Blood Grouping
 Blood types is based on the different types of antigens present on
the surface of the red blood cells (RBC).
 Four Groups: A, B, AB, O. The letters stand for the type of antigen
present on the red blood cells.
 The corresponding antibodies are carried in the plasma and if the
person has a particular antigen in his red cells, he can not have the
corresponding antibody, since agglutination would occur. Thus group
A contains antigen A and antibody anti-B.
 Group AB has antigens of A & B and not antibodies of either type.
 Group O has no antigens and antibodies anti-A and Anti-B.
 If the blood protein [first discovered in blood of Rhesus monkey] is
present in the blood cells, then the blood cells are called Rh
positive and if they are absent, it is called Rh negative.
Guidance for Children
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Air we breathe out is seen in cold day
 The air we exhale on a cold day is visible because of the formation
of dew.
 The air we exhale has water vapour and carbondioxide.
 Our exhale air is about 40oC but outside atmosphere is about 10oC.
 Cold air cannot hold as much water vapour as warm air. Dew is
formed when air is cooled to the point where it cannot hold all its
water vapour, so the moisture in it begins to condense forming tiny
water droplets. The temperature at which the moisture in the air
begins to condense is called dew point.
 From 40 to 10 degree centigrade, it is cooled to below the dew
point but above its freezing point. Hence the tiny water droplets
float in the air and are visible.
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Myopia
 Myopia is defined as an eye defect where the image of
the object falls before the retina of the eye.
 The person affected with myopia cannot see distant
objects clearly, but can see objects that are close to
him.
 Myopia is also known as short sight.
 Three types:
 Congenital Myopia: Since birth.
 Simple or developmental myopia: Defect increases usually as
age advances.
 Pathological or degenerative myopia: Condition rapidly
increases and there may be high myopia upto 20 D.
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Cramps
 Cramp can occur due to a localised muscle spasm.
 Pain or uneasiness is caused by nervous irritation due to
accumulation of some metabolites or chemicals in that
area.
 Massage, external compression of muscle, improves
blood supply. It helps in washing away these metabolites
and thus relives the cramp.
 However, not all cramps can be relieved by massage.
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Dandruff
 Dandruff is a condition of excessive scales of the scalp.
 There are two varieties: Dry and Greasy.
 Dry: The scales are fine, thin, white or greyish, and dry or slightly
greasy.
 Lacks lusture; Mild to moderate itching; Scales will fall freely on the
shoulders.
 Occurs more in winter than in summer.
 Exaggeration of normal exfoliation of the horny layer of the epidermis.
 Greasy: Both the scale and integument are oily.
 Extends to eyebrows, eyelids, beard and others.
 Basic defect in this case is over production and/or change in
composition of the sebaceous secretion.
 Common at puberty and it occurs due to endocrine disorders, familial
predisposition, unbalanced diet and constipation.
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Antidandruff Shampoo Work
 Dandruff is thought to be caused by overgrowth of yeast
such as Pityrosporum ovale which live on normal skin.
 Antidandruff shampoos work by three mechanisms:
 Ingredients such as coal tar are antikeratostatic and they
inhibit keratinocyte cell division.
 Detergents in the shampoo are keratolytic: they break up
accumulation of scale.
 Antifungal agents such as ketoconazole inhibit growth of
yeast itself. Other components such as selenium sulphide
also inhibit yeast growth and therefore scaling.
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Cold & Flu in Winter
 Rhinivirus, which is responsible for up to 40 per cent of clods,
culture better at a temperature of 32 degrees C rather than the
normal body temperature of 37 degrees C. However, 32 degrees C is
the normal temperature of the lining of the nose, which is good
news for the virus.
 Children and teenagers are far more susceptible to infection as the
immune system learns how to combat more infections as they get
older as have been exposed to more of the 200 or so viruses
responsible for the common cold.
 Densely packed nurseries, schools and college provide an ideal
breeding ground for viruses which then spread out into the
community aided by the cold damp weather.
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Hiccups
 Diaphragm is located between the chest and the stomach.
 While inhaling air this diaphragm goes down and presses the
stomach due to which the lungs are filled with air.
 While exhaling air, the diaphragm goes up and the air comes
out from the lungs.
 Thus the diaphragm goes up and down and the process of
respiration continues incessantly without making any sound.
 Two sudden and involuntary contractions within the
diaphragm cause hiccups. You can get hiccups if you eat too
much or too fast or if you eat victuals disagreeable to your
system.
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Blocking Nose While Crying
 Tear fluid is secreted by a lacrimal gland seen bulging
the conjunctiva (muscous membrane covering the
eyeball and lining the eyelids)
 Tear passes through numerous ducts into the
conjunctive sac, aided by ocular muscle contraction.
 From there it reaches the lacirne sac and through the
lacrimal duct it is drained into the nasal cavity,
(Lacrimal duct is an anatomical drainage canal connects
the corner of the eye to the lower surface of the nasal
cavity).
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Itching when wound heals
 Itching is due to the release of a chemical substance, called
histamine, which stimulates nerve endings.
 Histamine is a decarboeylated form of amino-acid histidine, a
powerful vasodilator present in animal tissues.
 When tissues become inflamed, histamine is released from
mast cells in the tissues.
 During healing, the number of basophils in WBCs increase.
Basophils contain relatively large amounts of histamine.
 Histamine from the basophils and from the surrounding cells
diffuse into the skin nearby and stimulates the nerve endings,
which leads to itching.
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49
Wound becomes Septic
 The reaction between metal sheets and air or other
oxidising agents are the cause for rusting.
 Rust is a form of oxidised metal film forms on metallic
surfaces.
 When these rusted metals make wounds, the microorganisms gain entrance into the wounds as spores and
germinate under unaerobic condition particularly when
the wound is deep or if the oxygen tension is low due to
the presence of other aerobic micro-organisms.
 During the metabolism these clostridia excretes toxins,
that are pathogenic for human beings, the wound
become septic and if left untreated results in death.
Guidance for Children
50
Burning Sensation using Dettol
 Tincture, dettol and other similar antiseptics act as
disinfectants and are corrosive in nature.
 When these antiseptics are applied on wounds, due to
their corrosive nature they damage the cell proteins in
the tissues.
 This action stimulates the underlying sensory nerves
leading to a sense of irritation.
 To reduce the corrosive action, use them in a diluted
form [live adding water to it].
Guidance for Children
51
Sleepy after heavy meals
 In the human body the mechanism is such that the oxygen we
breathe in and the vital nutrients in the food that we eat are
absorbed by the blood and supplied to the different organs.
 The amount of blood supplied to each organ depends on the oxygen
and nutrition requirement of the tissues of the organ and the
importance of the function it plays at any given time.
 Normally: one-third of blood goes to liver, one-fourth to kidney,
one-sixth to brain. Remaining goes to the muscles and other parts
of the body.
 With heavy meals, digestion of the food is needed and so more
blood is sent to the stomach wells. Automatically the flow of blood
to other parts of the body, including the brain, is reduced.
Guidance for Children
52
Yellowing of Urine
 Yellowing of urine is due to the predominant rise in the
unconjugated bilirubin in the blood.
 Administration of certain drugs in the patients can also
result in the rise of unconjugated bilirubin.
 Even some common medicines like paracetamol and
sulfonamide are hepatotoxin. So they cause mild
damage to the liver cells which results in the increase
of bilirubin level in the blood.
 In the case of tonics, yellowing is due to excretion of Bcomplex vitamins. These vitamins are water soluble and
absorption of these vitamins is very rapid. But they are
rarely stored in liver except vitamin B-12.
Guidance for Children
53
Vegetables washing and cooking
 When the cut vegetables are washed in water, the water
soluble vitamins (B complex and Vitamin C) are leached
away. So, wash before cutting.
 When vegetables are cooked, thermal destruction of
vitamins and nutrients also take place. So, over heating
of vegetables should be avoided.
 Frying and roasting is bad as it causes 40 - 60 per cent
nutrient loss.
Guidance for Children
54
Vomiting while Travelling
 Giddiness occurs when we lose our sense of balance.
 The sensations perceived by the eye, inner ear, skin,
muscles and joints help the body to know its stability.
 When we look down from a great height, abnormal
visual signs are transmitted to the brain, without any
corresponding information from other parts of the body.
 While looking out in a fixed direction while travelling in
a bus, the eye sends fast changing visual signals to the
brain. Such signals confuse the mechanism in the brain
and lead to giddiness and vomiting.
Guidance for Children
55
Blind men with improved capabilities
 Scientists have found that the brain is plastic – meaning,
the brain can rewire itself. This has proved beneficial to
the handicapped.
 Researchers have demonstrated the process of brain
rewiring using a technique called transcranial magnetic
stimulation in which they apply a magnetic field to the
skull and induce electric currents on the brain.
 They found that the visual cortex (the part of the brain
which handles signals from the eye) of a blind person’s
brain does not remain idle – other senses use it.
Guidance for Children
56
Atmosphere with stellar bodies
 Atmosphere of stellar bodies is determined by studying
the spectrum of the light coming from the stellar body.
 We know that the atmosphere is made of atoms and
molecules.
 Each of these atoms and molecules emit light at
characteristic frequencies or wavelengths which are
also called signatures. No two elements emit light of
the same frequency.
 Researchers use spectroscopic tools to study the light
coming from stellar objects and identify the frequency
of components in them.
Guidance for Children
57
Stars blink but not planets
 The stars seem to twinkle, because we see the stars through the
ocean of air, the atmosphere. The twinkling is caused by
differences in temperature in the air.
 Some layers of air are hotter than others, and one layer is always
swirling and moving through another. These different layers of air
bend the star light in different ways, and at different angles.
 Stars near the horizon seem to twinkle much more than those high
in the sky. This is because the light of these stars has to travel a
longer path through a thicker layer of atmosphere, and thus has
more chance to become disturb.
 More rays come to us from the surface of a planet than from the
surface of a star. The light from the planets does not waver as
much as that from the stars, the wavering of one ray of light is
counteracted by the wavering of another ray in another direction.
Guidance for Children
58
Refrigerator sound
 The sound from a fridge is due to the frequent switching
on and switching off the compressor.
 The compressor is controlled by a thermostat, a device
which is generally used to measure temperature.
 When the inside of the fridge reaches a present
temperature, there is no need to cool it further. So, the
thermostat sends a signal and cuts the power to the
compressor to stop its cooling function.
 When temperature increases and reaches the critical
temperature, the thermostat sends a signal to restore
the circuit and switch on the compressor.
Guidance for Children
59
Cool room with fridge open
 Open fridge will heat the room.
 Under normal circumstances, the heat from inside the
fridge is taken out by the compressor and let out in the
air behind the fridge.
 If the fridge is kept open in a closed room, the chillness
coming out through the front door of the fridge is
cancelled by the heated air coming from behind.
 In any electrical appliance, a part of the electricity
supplied is wasted as heat because of the principles of
thermodynamics. This heat will raise the temperature
of air inside the room.
Guidance for Children
60
Automatic wrist watches stop
 Automatic watches have a different mechanism: a rotor
which can rotate freely (like a free wheel in a bicycle).
 Our hand movements make the rotor rotate and wind a
coil spring. The rotor frees itself to the original position
after the winding. As a result the rotations of the rotor
tighten the spring. The watch works as the spring
releases very slowly.
 If the watch (spring) is kept idle for some time, there is
no rewinding of the spring, and so it stops functioning.
Guidance for Children
61
Pressure cooker
 Principle of a pressure cooker is cooking under increased pressure.
It is well known that food gets cooked fast at high temperatures.
 There is no possibility of heating the water beyond 100 degrees in
open vessels. Hence it takes a lot of time to cook the food.
 Boiling point increases with increase in pressure. Hence in pressure
cookers, the steam in not allowed to escape but enclosed with in
the vessel. As more water is converted into gaseous stream, the
pressure increases which in a feed back mechanism increases the
boiling point to well beyond 100 degrees enabling fast cooking.
 Normally the temperature reaches about 120 degrees inside the
pressure cooker.
 In order that the pressure does not reach very high values so as to
cause an explosion, a weight and safety valve are provided to let
out the excess stream. Also the body of the cooker is made of an
alloy which can withstand high pressures.
Guidance for Children
62
Draw more current with low voltages
 Current and voltage are not always in direct proportion.
 Electrical appliances are divided into two groups:
 Appliances such as electric irons and electric heaters which convert
electrical energy into heat energy.
 Appliances such as motors which convert electrical energy into
mechanical energy.
 In first group, the current drawn is proportional to the square root
of the voltage.
 In the second group, the current drawn is inversely proportional to
the applied voltage, that is, when the applied voltage is lower, the
current drawn will be proportionally higher, with the mechanical
power remaining constant.
 Motors operating at low voltages burn out because they tend to
draw unduly large currents which can not be carried by the wires
wound inside them.
Guidance for Children
63
Earthing Pin is Bigger
 Earth wire starts from the metal body of the appliance and ends
in the earth. So it should never come into contact with live
wire.
 In case the earth pin is connected wrongly with the live socket,
the user touching the appliance might receive an electrical
shock.
 Earthing pin is made longer than the other pins, so that it gets
connected the earth terminal first before the other pins (live
and neutral) make the contact in their respective sockets.
 In case there is a short circuit, as soon as the appliance is
plugged in, the current from the electrical appliance flows to
earth without harming the user. Hence it is always safe to install
thick high tension wires for earthing.
Guidance for Children
64
High Tension Wires - humming sound
 Air surrounding the conductors of a high voltage
overhead transmission line is normally an insulator.
 But at extra high voltages (66,000 volts and above), the
air in close proximity to the conductor tends to break
down under the voltage stress, along the length of the
conductor and itself becomes a conductor. This is known
as corona effect.
 This effect is seen as bluish violet light and audible
corona as a hum. Audible corona is common. Visual
corona requires a higher voltage stress.
Guidance for Children
65
Electric Line Tester
 It is used for testing alternating current (AC).
 In an electric line, ‘phase’ line gives out AC which has
both positive and negative components.
 In the case of a tester, when we touch its metal cap, a
very small amount of current being tested passes
through the neon bulb, a high resistance and through
the body to the earth which is at zero potential.
 In other words the body helps to complete the circuit
enabling the tester to glow. The high resistance inside
the tester acts as a safety mechanism by restricting the
amount of current passing through the body.
Guidance for Children
66
Bird not get electrocuted
 A bird sitting on a live wire will be electrocuted only if
electric current passes through its body.
 One wire which we call live will be at a potential of 230
volts which is called the phase wire and the other one
which we call the neutral wire will be at a potential of
zero volts.
 Immediately on sitting on the live wire the bird’s
potential will also be raised to 230 volts and if by an
accident it comes in contact with the neutral wire or
touches it, a current will pass through its body from the
live wire which is at a higher potential to the neutral
wire which is at zero potential.
Guidance for Children
67
Fan Wings Slightly Curved
 Fan wings, also called blades, are curved for optimum
air circulation which is determined by solidity ratio
which is the ratio of the area of the blades to the area
of the disc swept by them.
 If a flat plate is used as a blade, it will provide air
circulation no doubt but the volumetric flow will be less
compared to a blade which is suitably curved based on
an aerodynamic principles.
 The cross-section of a blade is in the form of a circular
arc and is called camber. It will vary from the root of
the blade to its tip. One can see the blade twisted from
the root to the tip.
Guidance for Children
68
Reduce power with slow speed in fans
 We can save power with the new electronic regulators but
not with the old regulators based on rheostats.
 Rheostats consume a fixed power all the time. If we select
the highest speed all the power is fed to the fan’s motor. If a
lower speed is selected, electric power proportional to
selected level is fed to the motor and the remaining power
tapped from the mains is wasted as heat in the rheostat.
That’s why when we run the fan at slow speeds for a long
time the regulator becomes hot.
 New regulators are made up of semiconductor device called
triac. Depending on the speed selected, the electronic
regulator draws, from the mains, only the required power.
Guidance for Children
69
Chokes and Starters in Tube lights
 Tube lights are discharge lamps. To initiate a discharge, it requires
a high voltage (about 1000 volts) several times the main voltage
(about 200V). To sustain a discharge it requires only about 100 V.
 Choke in an inductance. When current through an inductance is
abruptly interrupted it induces a high voltage. The interruption is
done by the starter which works like a switch. The high voltage
strikes an arc between the filaments at the ends of the tube light.
Once an arc has struck, the choke takes half of the mains voltage
and leaves the rest to maintain the arc.
 Choke has a core made of thin laminated silicon steel sheets. When
the sheets vibrate with the power frequency (50 Hz) or its
harmonics it generates noise.
 A starter is made of two electrodes one of them is a bimetallic
strip. When a tube light is switched on, the voltage between the
two electrodes produces a spark.
Guidance for Children
70
Incandescent light bulbs turn grey
 The greying of the inner surfaces of incandescent bulbs
is the result of gradual evaporation of tungsten from the
filament while the light is on. This evaporation
eventually makes the filament so thin it burns out.
 To reduce greying, a mixture of nitrogen and argon is
used today.
 A small amount of abrasive tungsten powder can be
placed in the bulb. Shaking it occasionally will remove
the grey coating from the surface to the glass.
 Greying can almost eliminated by introducing a small
amount of halogens iodine and bromine.
Guidance for Children
71
Shadows with tube light and lamps
 As light travels only along straight line paths, if
obstructed by any object, it creates a shadow.
 Filament bulbs are point sources, that is, the light
emanates from almost a single point and goes out
radially in all directions.
 In the case of filament bulbs, there is no light ray falling
on the shadowed area and so the shadow is harp.
 If the light from one end of the tube light causes a
shadow, there is a possibility for the shadowed area to
be lit by a light rays coming from the other end or part
of the bulb. Hence the shadow is blurred.
Guidance for Children
72
Photocopier
 Photocopier is an electromechanical device having a photoconductive
cylindrical drum made of cadmium, selenium or an organic photoconductive
material. (A photoconductive material changes its conductivity under light).
 Upon switching on the machine, the drum is positively charged and the
heating section, at the exit of the copier, with a teflon coated roller is
heated to 230 to 320 degrees Celsius by a heating lamp.
 An image of the document is reflected by various mirrors and lenses to the
drum. Depending on the intensity of the light received the photoconductive
material loses its resistance at varying levels on its surface. That is, the
positive charges on the drum are neutralised except in those areas
representing the image.
 This results in a latent charge image on the drum. A toner (negatively
charged) is then pumped to the drum. Based on the ‘charge map’ the toner
gets deposited and forms a ‘toner image’ on the drum. The drum then
rotates and prints this image on the moving paper and ‘fixes’ it at a high
temperature.
Guidance for Children
73
Radio signals with directions
 In radio sets, the problem of not receiving signals in
certain directions is felt in the medium wave band.
 This is because for this band they use a coil wound on a
ferrite rod as the antenna.
 Ferrite rod is directional in its sensitivity. It picks up all
signals that come in a direction perpendicular to its axis
and rejects them if they come parallel to its axis.
 Therefore the reception is entirely based on the
direction in which they reach the radio set.
Guidance for Children
74
Gravel on Railway Tracks
 Gravel used on railway tracks is known as ballast.
 It is used to dissipate the vibration produced by trains
travelling at high speeds.
 In effect, the gravel layer acts as a cushion and damps
the vibrations so that they do not travel long distances.
 If the rails are laid on a solid base, these vibrations can
travel long distances and lead to cracks on the base as
well as on nearby buildings.
Guidance for Children
75
No Sound in Vaccum but Light
 Sound is a mechanical wave but light is an
electromagnetic (EM) wave.
 Mechanical vibrations propagate by the actual
displacement of physical properties. Each particle
oscillates about its mean position in a synchronized
manner ot cause energy propagation in a mechanical
wave pattern.
 In EM Waves, electric and magnetic fields ‘oscillate’
about their mean zero in mutually perpendicular planes
and cause wave motion.
 Thus EM Waves doesn’t need a medium but Mechanical
waves need a medium.
Guidance for Children
76
Different Rods in TV Antenna
 The length of the elements and their arrangement depend on
the wavelength of the signal (local TV station). For good
reception, the antenna’s length should be half the
wavelength of the signal in metres.
 The gain of the folded dipole antenna alone will not be
much. To reflect the signal which are not intercepted by the
dipole, a reflector of length more than half lamba is fitted at
the rear end.
 It reflects the electromagnetic waves just as a mirror reflects
light waves. Normally, only one reflector is used because
additional reflectors do not significantly improve the gain. To
boost the gain, the signal is directed towards the dipole using
the director elements which are of length less than half
lamba.
Guidance for Children
77
Water Heater Coil – Heating Process
 Molecules of water that are adjacent to the heating coil
first gets heated and thereby becomes less dense.
 The water of lesser density will move up due to which
the high density cool water on the surface comes down.
(Liquid of low density will always be at the top than a
liquid of high density).
 This movement of water molecules causes water at the
upper level to become warm sooner than the bottom
level though we put the coil at the bottom.
Guidance for Children
78
Global Positioning System
 GPS is a system which shows the exact position on the earth,
anytime in any weather and any where.
 There are 24 GPS satellites orbiting at 11,000 nautical miles above
the earth.
 GPS has 3 parts:
 Space segment consists of 24 satellites.
 User segment consists of receivers which we can hold in hand or mount
in a car and this gives the exact location on the earth.
 Control segment consists of ground stations that make sure that the
satellites are working properly.
 Receiver detects the time signal and calculates the distance of the
satellite. By getting signals from three different satellites and by
doing mathematical calculations, the receiver is able to give the
exact position where the receiver’s located.
Guidance for Children
79
Milk Overflows but not water
 Milk is of water (83 – 87%), protein (3.5%), sugar (5%)
and fat (4 – 7.4%).
 When milk is heated, fat boils lighter than water, floats
as a creamy layer on the top and water vapour, in the
form of steam bubbles, is trapped under it.
 Further heating results in the formation of more number
of bubbles.
 These bubbles expand and lift the creamy layer causing
it to overflow. In the case of water, the steam bubbles
break as they reach the surface.
Guidance for Children
80
Candle lights a room but no LPG
 Yellow light in candle is responsible for illumination of the room.
 Combustion (burning of fuel) can be of two types:
 Complete: Sufficient quantity of oxygen for the fuel to burn. This
results in a blue frame and the heat generated will be maximum.
 Incomplete: Oxygen supply is insufficient. This results in an yellow
frame with heat produced is lesser than maximum obtainable from the
fuel.
 Candle flame has blue [hottest zone surrounding the wick], black [unburnt
volatile fuel] and yellow flames.
 Yellow flame has hot carbon particles which get heated by hotter zones
below and emit light due to incandescence.
 LPG (Liquified Petroleum Gas), which is mostly propane and a little
butane, is mixed with sufficient quantities of air in the burner and then
burnt to give a blue flame.
 Propane needs about 25 times its volume for complete combustion. The
flow of gas in controlled and ratio of gas and air is maintained. As there is
no incandescent zone, the flame does not illuminate the room.
Guidance for Children
81
Information on Audio & Video Tapes
 Information is stored in audio/video tapes by magnetizing them.
These tapes are actually long, thin plastic films coated with a
magnetic material, mainly iron oxide.
 Player has a recording head which consists of a coil of a wire wound
around a circular piece of iron with a small gap. Any current passing
through the wire would produce a magnetic field around it.
 When the tape is run through the small gap present in the recording
head, the varying magnetic field magnetism the particles on the
tap rearranged their moments in accordance with the variation in
the input signal.
 While playing, the tapes is run past the recording/playing head
which senses the magnetic field along the tape. This induces a
varying current in the coil . This current is amplified and fed to the
speaker or TV to reproduce the original message.
Guidance for Children
82
Popping Ears in Aeroplane
 To maintain fuel economy, aircrafts should fly at altitudes far in
excess of those capable of sustaining life.
 Whereas 5500m is about the maximum altitude at which a person
can live for any extended period, a subsonic passenger jet has the
best fuel economy when flying at around 12000m.
 Therefore, aircrafts have to be pressurised the interior of a
passenger aircraft.
 All airfields are not at the same altitude.
 As for ear popping, for our safety and comfort the internal pressure
is imperceptibly reduced, all under computer control, as the
aircraft climbs. It is gradually increased during descent so that, as
the aircraft is coming to a stop on the runaway, the pressure inside
and out is the same. Normally, it is sufficient for your ears to
adjust. If not, pinch your nose and gently but firmly increase the
pressure in the nasal cavity until you feel the pressure equalise.
Guidance for Children
83
Cola Foam Up
 Carbonated beverages when opened and released from
pressure or supersaturated solutions of gas with more
carbon dioxide dissolved in the beverage than would be
possible at normal pressure.
 Left alone for two hours, the drink would slowly lose
the gas and go flat. Sodium chloride particles seem to
provide an especially good surface for gas to collect on,
form bubbles and quickly rise to the surface and
escape.
Guidance for Children
84
Ornaments of Pure Gold
 Ornaments could be made of pure gold but would get easily pressed
out of shape. This is because gold is a soft metal, though it is
heavy.
 Gold has high density, over two times that of iron, because its
atoms are heavier.
 A steel knife cannot cut glass, but a diamond tipped steel knife
could, because diamond is harder than glass and steel is not. Gold
is easily scratched.
 A bit of copper is added to gold, to give the ornaments hardness
and to prevent distortion.
 24 carat means 100 per cent gold. One carat represents 100/24 per
cent. 22 carat gold means 91.76 per cent of gold. Rest is copper.
Guidance for Children
85
Hard Water and Layer on Utensils
 Water contains dissolved salts of calcium, magnesium
and often iron in the form of bicarbonates, chlorides
and sulphates present in the Earth’s crust. When such
water is heated, the bicarbonates of calcium and
magnesium decompose evolving carbon dioxide and
leave behind sparingly soluble carbonates.
 Bicarbonates of iron interacts with the carbon dioxide
and water forming sparingly soluble ferric hydroxide
(brown). These sparingly soluble salts form the layer or
‘scales’ seen in utensils and boilers.
Guidance for Children
86
Cold water extinguish fire faster
 If we use hot water to extinguish fire, the heat
absorbed from the source (fire), by a definite quantity,
to reach its boiling point will be far lesser vis-à-vis the
same quantity of cold water.
 Colder the water, faster would be extinction of the fire.
Guidance for Children
87
Boiled Water lose Taste
 Natural water contains few substances [gases like
oxygen, carbon dioxide, sulphates and carbonates of
calcium and magnesium, iron, etc] that impart not only
taste but also hardness to it.
 Due to boiling, the dissolved gases are released and
hardness is removed. Insoluble carbonates and
hydroxides are formed which get deposited on the
surfaces and the bottom of the vessel as scales. Their
separation from water deprives it of its taste.
Guidance for Children
88
Air-Cooler and Air-Conditioner
 Air conditioning system is the system which keeps on
control and maintain the particular condition (this is
required temperature and humidity of air) in the closed
space.
 It is technically defined as a system which controls
temperature, humidity, purity and motion of air to
produce desired effects upon the occupants of the
space.
 In case of air cooler, which has the capability to cool
the air inside the space does not maintain particular
temperature and humidity of that air. In response to
atmospheric seasons we can have winter, or summer airconditioning system, but any air cooler will not do so.
Guidance for Children
89
Black box in Aeroplanes
 Black boxes which usually hold the clues to a plane’s crash, are
built strong enough to survive bomb blasts, violent impacts and
intense fires.
 They measure approximately 4 by 6 by 8 inches and weigh about 30
Kg and are kept in a case which can withstand 30 minutes of 1100
degrees C at 50,000 (Btu’s) British Thermal Units per square foot
per hour.
 Actually orange in colour and a very high quality heat resistant
paint is used, so that they can be spotted easily even at dimly lit
crash sites. They are always places in the tail end of the flight.
 Black box records voice and flight data.
 Cockpit voice recorder: Collects data and retains a record of the most
recent 30 minutes, the conversation between the pilot and Ground
Control Room.
 Flight data recorder: Records most recent 25 hours of a plane’s
operating data, including altitude, air speed, vertical acceleration and
heading.
Guidance for Children
90
Biscuits loose crispness in cool air
 Moisture content in fresh biscuits is about five per cent
after baking resulting in crisp texture and good storage
stability.
 When they are left open in air, they absorb moisture
and lose their crispness. The relative humidity in the
atmosphere can vary from about 40 per cent (during
summer) to 90 per cent (on a cool, rainy day).
 Inside a fridge, the temperature is kept low by cooling
the air. The water molecules present inside the fridge
condense on the cooling coils (evaporator coils) and so
the humidity is also low (the air is moisture-free). The
moisture appears as frost. As a result the biscuits
remain cool as well as crisp.
Guidance for Children
91
Layer on top of hot beverages
 The layer that forms on top of hot beverages consists of
fat.
 In unheated milk the fat globules are surrounded by a
thin film of protein, phospholipids and neutral fats.
 When the milk is heated, this thin film breaks, making
the fat globules free. These then coalesce on the
surface which then come to contact with the air and
forms a layer.
Guidance for Children
92
Beverages of Feeling fresh
 Most of the beverages contain alkaloids which act as mild stimulants.
 Caffeine in Coffee, Theophylline in Tea, Cocaine in Coco Products.
These alkaloids are collectively referred to as methyl xanthines.
 They share a number of pharmacological actions of much therapeutic
interest: they relax, smoothen the muscles (notably bronchial
muscle), and stimulate the central nervous system and cardiac
muscle.
 They induce the kidneys to excrete more urine, stimulate mental
activity, quicken the reflexes, increase vigilance and decrease motor
reactions time in response to both visual and auditory stimuli. They
increase stamina and reduce fatigue. They give the users a feeling of
confidence and power. They even induce euphoria in some users.
These stimulant effects a short lived: they last for about an hour.
They are then subsequently followed by depression.
Guidance for Children
93
Pencil Eraser
 A pencil mark actually consists of graphite particles abraded from
the pencil point by the paper.
 These particles, which have an angular, gritty look under the
microscope are, for an HB lead pencil, typically between 2 and 10
micrometres in diameter.
 The particles lie slightly below the surface of the paper, interlocked
between its fibres.
 A single rub using a rubber sufficiently soft to reach between the
fibres will pick up most of them. Inspection of the rubber shows the
undamaged particles adhering to the surface.
 An effective erasing material is also abraded by the paper surface,
producing the familiar small spindles of rubber or eraser material,
which wrap up the graphite particles.
Guidance for Children
94
Stick to walk on ropes
 While walking on a rope, as the base is very thin (as thin
as the rope), to be stable the artist has to move his
centre of gravity appropriately. This he does by holding
a bamboo pole horizontally or using an umbrella or just
by spreading his hands?
 When the artist feels that he is falling to his left, he
moves the pole to his right (and vice versa) and
counters the forces disturbing his balance and makes
the centre of gravity fall within his base.
Guidance for Children
95
Mehndhi impart color
 Human skin is made of four layers – the tipmost layer is
stratum corneum, followed by epidermis, dermis and
sub-cutaneous layers.
 When mehndhi is applied on the skin, the red pigments
present in it are transported along with water through
the small pores in the stratum corneum. As the hand
dries, the water evaporates leaving the pigments which
impart the colour.
 In nails, the pigments are trapped between the horny
plate like cells which are piled in lamellar layers. Pores
in skin are larger than those in nails. This actually
accounts for rapid fading of colour in skin compared to
that of the nail.
Guidance for Children
96
Blind Feeling in Dark Room
 Seeing in dark involves two types of cells – rods and cones, in the
eye.
 These cells are present in the light-sensitive innermost layer of the
eye called the retina. They lie in front of a pigmented tissue layer.
Cones are present in the area of greatest visual activity – fovea
centralis, which lies at the centre of small yellow pigment spot
behind the pupil. Rods and cones are present around the fovea.
 Cones are active under intense illumination, whereas rods are
active in dim light. In the dark, rods are sensitised by a pigment
called rhodopsin or the visual puple that is formed within the rods.
Rhodopsin is bleached by light and is reformed by the rods in
darkness. Hence a person who steps from sunlight into a dark room
experiences a blinding feeling till the pigments being to form.
 Cones adapt themselves to fainter light in the ambience of low
intensity illumination, which may take around five minutes.
Guidance for Children
97
Closing Wooden Doors in Winter
 When dry wooden pieces and seeds of certain species
are put in water, they absorb water and swell
noticeably. This phenomenon of water absorption is
called imbibition.
 Imbibition is due to the presence of large number of
hydrophilic colloids in both the living and dead cells of
wooden materials.
 During rains, relative humidity of atmosphere air is
high. Hence, wooden doors absorb water molecules and
swell. If the clearance between the door frame and
door is insufficient to accommodate the swell, we
experience difficulty in closing and opening it.
 Periodic painting helps to reduce moisture absorption
Guidance for Children
98
Glass Tumbler breaks with Hot Water
 Glass tumblers break due to the difference in thermal
expansion of their inner and outer surfaces.
 Glass is known as a bad conductor of heat. Hence when
the tumbler is suddenly filled with hot water, the inner
layer of glass gets heated immediately as it comes into
contact with the hot liquid. But the outer layer remains
at a lower temperature for some more time as the heat
is conducted through the glass only slowly.
 As a result, the inner layer tends to expand more than
the outer layer. This leads to cracking. Thick-walled
tumblers and tumblers made of special quality glass
withstand such cracking to a certain extent.
Guidance for Children
99
Noise Shatter Glass
 Noise (a mixture of sound waves of varying frequencies) generated by
the vehicle sets up vibrations in the atmospheric air surrounding it.
 These vibrations (sound waves) transfer the energy from the source
(vehicle) to the surrounding and dissipate it. If the noise is not
intense, the sound dies away with in a short distance.
 If it is intense, the waves travel long distances. When these waves
come across solid objects such as window panes, they transfer their
energy to the object and force them to vibrate.
 If the frequency of the sound wave matches with the natural
frequency (Any object will have a natural frequency of vibration which
depends on the nature of the material) of the object, resonance sets
in the object begins to absorb the incident energy and forced to
vibrate with large amplitudes. In case of window panes, its edges are
held (if not tightly) by the window frame which prevent the
oscillation. This results in shattering.
Guidance for Children
100
Shaving Brush Give More Lather
 The bristles of a shaving brush are bunched together to
ensure that there are a large number of thin columns of
air in-between them. When the brush is moved to and
fro, the soap solution seeps into the brush, due to
surface tension, partially filling the air columns.
 While shaving, the soap solution stuck to the skin is
dragged to from thin films. But when stretched beyond
a certain length, limited by surface tension, the films
break and in that process trap a little bit of air to form
small bubbles. As there are hundreds of bristles involved
in the bubble making process, we get lather within a
short time.
 The same principle applies to tooth brush and the
Guidance for Children
101
Verify Purity of Honey
 Honey is adulterated by way of adding jaggery syrup.
 To verify whether honey is pure, take a glass of
waterand pour one tablespoon of honey in it.
 Gently shake the glass (note not to stir).
 If the honey completely dissolves in water it is
adulterated.
 On the other hand if it stays as a mass, it is pure honey.
Guidance for Children
102
Kite Flies but not Paper
 Obviously because of the string and the tail.
 First, the sheet of paper is made stiff using thin sticks so that it does
not bend due to the forces of the wind.
 Next, 3 – 4 small strings of equal length are attached. All this is to
make the kite fly at an angle with the direction of the wind.
 Force acts in two components – one horizontal and the other vertical.
Generally, the vertical component lifts the object (against gravity)
and the horizontal component pushes the object (along the direction
of the force). Here the force acting on the kite is due to the wind.
 In kite: kite is held by string in one direction (a restoring force) and
the wind is exerting its force in opposite direction. At times we pull
the string or run into the wind. These are tricks to increase the lifting
force and make the kite fly higher. Some kites tend to rotate along
the axis of the string. To prevent this rotation, a long tail is attached.
Guidance for Children
103
Aeroplanes and lightning
 Clouds are made of water droplets and dust in the atmosphere at
altitudes of 1 to 16 Km. While travelling through air, due to
friction, the water droplets get electrically charged.
 Lightning occurs due to sparking between oppositely charged clouds
– a high voltage spark rushes towards the ground (at zero potential)
through moisture filled air.
 If any ground based structure is on the path of the spark, the top of
that structure is excited to a high electrical potential while its
bottom (in contact with the ground) remains at zero voltage. This
high potential difference sets a very high current in the structure
causing sudden heat generation in the material and destruction.
 But in flying aeroplanes, there is nothing like a ground point which
remains always at zero voltage. Thus if hit by lightning, the plane’s
entire surface acquires same high potential and due to lack of
potential difference there is no current and so no destruction.
Guidance for Children
104
Blotting Paper Absorb Ink
 Blotting paper absorbs ink by capillary action which is a
natural phenomenon exhibited by liquids in the
attempts to reduce surface tension.
 Blotting paper is made of cellulose obtained from the
pulp of cotton linter, wood or straw. A purified pulp
paste is directly pressed to form blotting paper sheets
without any treatment. So as to incorporate microscopic
capillaries. When such a paper is placed in ink, water or
any aqueous solution, the solution immediately enter in
to these capillaries and spreads all over the sheet.
Guidance for Children
105
Train Stops when Chain is pulled
 Trains are equipped with vacuum brakes.
 Pipes passing through the underside of coaches are connected to
vacuum cylinders (provided in the coach) which help maintain a
vacuum throughout the length of the pipe. The pipes (of each
coach) are then linked.
 When the driver wants to stop the train, he gradually allows air to
enter the vacuum pipe and activates the pistons of the vacuum
cylinders which help to apply the brake.
 For emergency application of brakes by passengers, coaches are
provided with alarm chains connected to the vacuum system. When
the chain is pulled, a small valve opens up and allows air to enter
the system slowly, gradual application of the brakes.
 Direct admission valves are provided in each coach near the
vacuum cylinder and they help in the uniform application of the
brake throughout the train.
Guidance for Children
106
Sound with Thumb and Middle Finger
 A small amount of air is trapped and pressurised when
the fixed end of the thumb and the free end of the
middle finger are brought together.
 When this pressurised air is released suddenly during
the clicking, it produces a sound as in the case of a
balloon burst.
Guidance for Children
107
Watching TV
 If one sits too close to the television or cinema screen, the eye lens
has to do more frequent focussing for viewing. Light rays from a
near portion of the picture diverge and so the lens is curved more
to focus on them.
 Simultaneously, the lens has to collect the light (coming more
parallely) from more distant parts of the picture. This causes strain
on the eye, and if practised for long, can permanently damage the
eye.
 Width-to-height ratio of TV screen is kept as 4:3 because of the
binocular vision due to the pair of eyes in the horizontal plane and
the range of movement of both the eyeballs being less restricted in
the horizontal plane as compared to that in the vertical plane.
 The best viewing distance for watching TV is 4-8 times the height of
the screen.
Guidance for Children
108
Hearing Audio when TV Switched on
 When TV is switched on, electric power is supplied to
both audio and video sections.
 The video section consists of a cathode ray tube which
is called as picture tube. An electron beam is used to
sweep the screen to display the pictures. This electron
beam is generated within the CRT using a filament
which can emit electrons only when heated. This
heating process requires some time.
 Audio section does not need any such ‘warm up’ to start
functioning and so we hear the sound as soon as we
switch on.
Guidance for Children
109
Tear Gas
 Tear gas is a noxious gas. It is also called as war gas since it is used
to disperse soldiers in a battle and an attacking mob.
 It is one kind of Lachrymator. Firing certain chemicals in artilleries
or pen gun produces it. The chemical substance used is, either
alpha chloracetatophenone, a solid material or ethyliodoacetate, a
liquid material.
 Tea gas vapours cause irritation of eyes in with a copious flow of
tears, spasm of eye lids and temporary blindness.
 Persons exposed to tear gas should be removed to fresh air and
they should wash their eyes with normal saline or boric acid
solution. Weak sodium bicarbonate solution should be applied to
the affected parts of the skin.
Guidance for Children
110
Not to drink distilled water
 Distilled water contains some dissolved gases like
carbon dioxide.
 Distilled water as such is harmful, if drunk.
 Because it contains no dissolved materials, it has a
tendency to dissolve the tender mucous membranes on
our mouth, etc.
 Warm water, especially if it is free of dissolved
materials, will have a corrosive action on the delicate
mucous membranes.
Guidance for Children
111
Changing water in aquarium
 Fishes use their grills to separate the oxygen from water
and release out carbon dioxide.
 In lake or pond, there is not much considerable change
in Oxygen level because: in a huge amount of water
only negligible ratio of oxygen is used. Direct and
indirect rainwater keeps the oxygen ratio stable.
 Water plants like Hydrilla and Vallisneria use the carbon
dioxide and deliver oxygen during their photosynthetic
activity. But in aquarium, there is less amount of water
and there are not natural plants to maintain the oxygen
level. Another reason for changing the water is to keep
the water clean from the fish waste in aquarium.
Guidance for Children
112
Water Inside Coconut
 Coconut water is the endosperm part of the coconut plant.
 In a very young coconut fruit, the endosperm is found as a clear
fluid in which float numerous nuclei of various sizes. This fluid is
compactly filling the embryo sac in which the embryo is
developing.
 At a later stage, free nuclei start settling at the periphery of the
cavity and layers of cellular endosperm start appearing. This forms
the coconut meat. This meat is very tender enclosing the fluid
content called coconut water. It is called tender coconut.
 The quantity of cellular endosperm increases further by the division
of cells. In mature coconut the liquid endosperm becomes milky
enclosed by the cellular part called kernel and it does not contain
free nuclei or cells.
Guidance for Children
113
Energy of raw and boiled rice
 Energy content of raw rice is 3620 cal/kg with 12 per cent
water content whereas that of boiled (cooked) rice is 1098
cal/kg with 73 per cent water content.
 Parboiled rice: Parboiling is a hydrothermal treatment
followed by drying before milling for the production of milled
parboiled grain.
 During parboiling, the B vitamins and minerals from hulls,
bran and germ will be leached into endosperm and hence loss
during polishing is minimised.
 Energy content of parboiled raw rice is 3703 cal/kg with 10
per cent water content whereas that of boiled (cooked)
parboiled rice is 1057 cal/kg with 73 per cent water content.
Guidance for Children
114
Refrigeration and Freshness
 Vegetables when allowed to stand for a long period after gathering, they
become wilted through loss of moisture by transpiration. This process
affects the commercial and physiological deterioration of fruits and
vegetables after harvest.
 Moisture loss adversely affects the appearance, texture, flavour and
weight of the products.
 Tropical vegetables and a variety of greens should be stored between 8
and 120C. At this temperature, the rate of metabolism of these vegetables
is still considerably high, which reduces both quality and storage life. So
refrigerated storage should be well supplemented with Modified
Atmospheric Packaging (MAP). User perforated poly-packages that can
maintain desired oxygen and carbon dioxide within the packages.
 Commercial storage of fruits require 00C with preferred relative humidity
of 85%. Fruits stored in home refrigerators tend to lose moisture. To
prevent this, the fruits must be kept in ventilated covered containers,
enabling the circulation of air around sides, tops and bottom of the fruits.
Guidance for Children
115
Mouth Sink After Sleep
 Bad breath or ‘Halitosis’ is a common problem, which often occurs due to
bacterial activity in the mouth.
 Halitosis, also termed ‘oral malodour’ is a foul or offensive odour emanating
from the oral cavity.
 Local source of mouth odour is mainly the tongue. Post natal drip on the back
of the tongue which occurs during sleep can also cause oral malodour in the
mornings and can cause throat infections in some cases. A coated tongue is
also said to be a cause of halitosis, due to excessive bacterial activity on the
tongue. The cause of bad divided into Intraoral sources (sources inside the
mouth which can cause bad breath), Extraoral sources (sources outside the
mouth or anywhere else in the body).
 Intraoral sources include retention of odoriferous food particles on and
between the teeth, coated tongue and dehydration states which can cause
dryness of mouth leading to oral malodour caries.
 Periodontitis (inflammation of the tissues surrounding the teeth) is one
condition if left untreated can cause bad breath from accumulated debris
and increased rate of putrefaction of the saliva.
Guidance for Children
116
Humans Brush But Animals Don’t
 Teeth are hard white structures found in the mouth of
humans and in many other animals and are usually used
for mastication.
 Animals need not brush their teeth due to the
adaptation of their teeth. For eg., the teeth of snakes
are very thin and sharp and usually curve backward.
They function in capturing the prey and not in chewing.
The teeth of carnivorous mammals for eg. Cats and dogs
are more pointed and adapted to cutting and shearing.
 For carnivorous animals, chewing is not essential. Their
teeth come into play only during cutting and shearing
their prey. Animals cells in meat are not encased in cell
walls and can be acted upon by digestive enzymes.
Guidance for Children
117
Drink Of Marine Mammals
 Marine mammals do not actually drink.
 They get all their water from the fish that they eat.
 They come dehydrated very quickly if they are not
feeding adequately and, when in captivity or care, they
must be fed from a pipe or bottle if they are not eating.
Guidance for Children
118
Astronauts breathe in space
 People on the space station get oxygen for breathing in two ways.
The first way is to make oxygen from water by zapping it with
electricity (electrolysis). Each molecule of water contains two
hydrogen atoms and one oxygen atom.
 Running a current through water causes these atoms to separate
and recombine as gaseous hydrogen (H2) and oxygen (O2). This
makes oxygen gas and also hydrogen gas. The other way is from
large tanks of compressed oxygen mounted on the outside of the
airlock module of space station.
 While astronauts moving out from the space station use standard,
off-the-shelf breathing air devices incorporated inself-contained
totally encapsulating suits. They also breathe using ‘perchlorate
candles’, which produce oxygen via chemical reactions inside a
metal canister. (‘Perchlorate’ is packed inside the canister). Each
canister releases enough oxygen for one person for one day.
Guidance for Children
119
Feel Sleepy while Reading
 Feeling sleepy while reading for many is due to the
posture in which they read.
 While reading a person rarely moves, this lack of
physical activity causes decreased blood flow of
muscles, which results in accumulation of lactic acid (a
product of incomplete combustion in the cells).
 This lactic acid is a highly reducing or oxygen absorbing
agent, which quickly reacts with oxygenated blood. This
ensures lack of oxygenated blood flowing to the brain,
which makes us feel sleepy.
 To tackle this problem we must avoid reading in a single
stretch, instead its better to take some breaks and
indulge in physical activity at short intervals.
Guidance for Children
120
Anti-Perspirants
 Perspiration, or sweat, is our body’s way of cooling itself, whether
that extra heat comes from hardworking muscles or from
overstimulated nerves.
 Sweat does not ‘stink’ but it is only after bacteria eat the sweat
that this excretions ‘stink’.
 Deodorants mask the smell of body odour, which is actually caused
by bacteria, whereas anti-perspirants block the pores of the skin to
stop us from perspiring.
 Most antiperspirants contain aluminium chlorohydrate/aluminium
chloride or aluminium zirconium, which are highly soluble and
readily absorbed into the skin. Once in the body, the aluminium
passes freely across cell membranes and is readily absorbed. When
the aluminium ions are drawn into the cells, water passes in with
them. As more water flows in, the cells begin to swell, squeezing
the ducts closed so that sweat cannot get out.
Guidance for Children
121
Eau-do-Cologne and Fever
 We have temperature signals in the peripheral areas of our body. These
areas are found especially in the skin and certain deep body tissues. These
centres contribute very significantly to body temperature regulation.
 Set point is the particular temperature at which sweating begins.
 Hypothalamic temperature or core temperature is 36.7 to 370C, when skin
temperature is 330C.
 When the skin temperature rises above this, due to warm weather and
other reasons, immediately sweating begins. So when the skin
temperature is very high sweating begins at a lower core temperature.
 On the other hand, during high fever both the skin temperature and core
temperature begin to rise. Skin temperature will be above 330C and core
temperature will be above 370C. Sine the core temperature is above
normal sweating will not occur and so there will not be loss of body heat.
But when the skin temperature is reduced to 290C we can induce sweating
even at much high core temperature. This can be done artificially by
applying eau-de-cologne, which is a cooling agent.
Guidance for Children
122
Temperature of Planets & Stars
 Astronomers now take the entire electromagnetic
spectrum into account, not just visible light. In general,
cool objects give off radiation of long wavelengths while
hotter objects give off short wavelengths.
 Infrared telescopes sent into space far beyond the
obscuring atmosphere of Earth measure the short
wavelengths below those of red visible light, and X-ray
and gamma ray telescopes are trained on longer and
longer, and hotter and hotter, astronomical objects and
events.
Guidance for Children
123
Humming in Thermos Flasks
 Humming sound heard in thermos flasks is due to the phenomenon of
resonance.
 Background noise present in the atmospheric air acts as a source of energy
(sound energy). Physicists call this as white noise as it is a mixture of all
possible frequencies ranging from 20 Hz to 20 kHz which are audible to us.
 This noise may not be audible to us because of their very low intensity.
 When these sound waves encounter a cavity like that of a flask they are
‘filtered’, that is, only sounds of particular frequencies (determined by the
inner dimensions of the flask) are allowed to enter freely into the flask’s
cavity, and other sounds are simply reflected in the outside.
 Hemoltz resonator is an acoustic device used to pick up and amplify a
particular frequency equal to its own natural frequency from a mixture of
sounds.
 Flask has very little damping factor (because of its highly polished inner
surface) and so vibrations get reflected inside without much loos of energy.
Due to resonance, this particular sound wave gets amplified and becomes
audible.
Guidance for Children
124
Immediately switch on and off
 Don’t switch on immediately after switch off.
 In fridge:
 Expansion device that changes the pressure refrigerant into low
pressure is a simple capillary tube. When the fridge is switched off the
compressor stops working and the refrigerants slowly down to the
evaporator. If the system is switched on immediately, the compressor
starts under ‘no load’ condition. Refrigerator uses low-power motors
along with compressors to reduce cost. A small wait period (a few
seconds) is needed to allow all the refrigerant to flow into the
evaporator.
 In TV:
 Problems arise due to transformer which holds a stray magnetic field
for a short duration, even after switch off. If we switch it on
immediately, the field set up by the power supply will interfere with
the stray magnetic field and reduce the efficiency and the life of
appliance. With a few seconds wait period, this could be avoided.
Guidance for Children
125
Refrigerator Capacity in Litres
 Capacity means the place occupied by a certain thing.
 Usually weight of different things/items will not agree
with the same capacity. i.e., weight of 250 litres of
water is less than the weight of 250 litres of oil.
 However if they are poured into a container of 250
litres, they would occupy the full container.
 Hence capacity is concerned with the place occupied by
the things and not with their weight.
Guidance for Children
126
Vehicle Crossing and Flickering TV
 Two wire transmission line has two wires of conducting material
running parallel to each with air as the dielectric mediate.
 The waves travelling through this are electromagnetic in nature. So
when a vehicle (having spark plug) crosses the place the spark from
the plug creates an electrical disturbance. This electrical wave
interferes with the electromagnetic wave in the transmission line
and as a result one gets disturbances on the screen.
 In coaxial cable (used by satellite TV channels), inner and outer
conductors are separated by a solid dielectric media. So when the
electrical disturbance from a vehicle interferes with the
electromagnetic waves in the cable they reach the outer conductor
easily but when the passing onto the inner conductor they are
offered a resistance by the dielectric media (mostly mica).
Guidance for Children
127
Lightning affect TVs
 Lightning is actually a sudden discharge of high voltage
and high current arising out of large voltage (potential)
differences between charged clouds.
 These surges, in their path towards the earth, can strike
power lines and antenna and pass through the wires to
terminal equipment such as TV.
 Huge currents and voltages, even though of short life,
can damage the electrical components and electronic
circuits which are usually designed for low power. The
surges are so powerful that they can destroy the
equipment even if they are off but connected to the
mains/antenna.
Guidance for Children
128
Electric Current Causes Death
 Electrocution depends on the amount of current that flows through or over
the body.
 High voltages (higher tensions) may cause the person to be thrown, while
lower tensions, around 240 volts, cause muscle contraction due to which
person holds on to the source of the current. This is also dangerous, because
severity is directly proportional to the duration of current flow.
 Dry skin offer high resistance but the resistance is diminished when the skin
is moist or covered with sweat. Blood has a low resistance and as such within
the body, electricity tends to be conducted along blood vessels. The intense
heat, which may results from flash over produces burns. High voltage burns
may be severe with charring of the body. If the area of contact is relatively
large, e.g. when a hot wire is grasped with a wet hand or when a person is
electrocuted in a bath tub, death may occur without any visible skin burning.
 Electrocution also depends on the path of the current in our body. Death is
more likely to occur if the brain stem or heart is in the direct path of the
current.
Guidance for Children
129
SIM Card Function in Cell phone
 It is a plastic card, which is called a subscriber identity module
(SIM). It consists of an integrated microprocessor chip, which keeps
data relating to a subscriber, and provides communication with GSM
network.
 All GSM cellular communication telephone cells are performed via
these antenna and stations, which are regulated by switching
centre. Switching centre provides communication between city
telephone network, base stations and other cellular communication
operators. Every time you switch on your cell phone, the
communication is performed with the nearest base station. At the
same time permanent receive-transmission of signals from your
terminal is performed.
 SIM card serial number is printed on its backside. This number
contains the information necessary to obtain a new card, in case
SIM card or GSM phone is lot or stolen.
Guidance for Children
130
HAM Radio
 HAM operators are amateur radio operators duly licensed by
the government to operate their own small wireless
transmitters purely as a hobby to develop their scientific skill
particularly in wireless communication and not for any
pecuniary benefit.
 To be a ham, we need to pass an exam in basic electronics,
operational procedure and Morse code conducted by Ministry
of Communication, Government of India. Each one is assigned
a distinct number called ‘call sign’.
 Short wave communication is one the important findings of
amateur radio operators. One can monitor the conversation
between hams using an ordinary radio set at 7 MHz frequency
(41 metre band).
Guidance for Children
131
Diamond Sparkle more than Glass
 This is a phenomenon of total internal reflection of light, dependent on the
‘critical angle’ of the incidence of light in a material medium at its bounding
surface with air.
 When a ray of light travels from a denser medium to a rarer medium, the
refracted or deviated ray is bent away from the normal (perpendicular) on
the interface of the two media. For a certain angle of incidence, the
refracted ray becomes parallel to the bounding surface or angle of refraction
is 90 degrees. This angle of incidence is called critical angle. When the angle
of incidence is further increased the ray is totally reflected back in the
denser medium. This phenomenon is called total internal reflection.
 The higher the refractive index of a transparent material the smaller is the
critical angle and hence the larger is the range of angles of incidence of
more light to be totally reflected. A diamond has a large refractive index and
very small critical angle as against glass.
 Light entering diamond from different faces, suffers multiple total internal
reflection and comes out of the diamond as intense beams from selected
directions. Hence, the diamond shines brilliantly.
Guidance for Children
132
Touch Screen Works – 1 of 2
 You can use your finger on the computer screen to
navigate through the contents.
 A basic touch screen has three main components: a
touch sensor, a controller, and a software driver. The
touch screen is an input device, so it needs to be
combined with a display and a PC to make a complete
touch input system.
 Three systems:
 Resistive: Made of Conductive and Resistive metallic layers with
spaces in between. Electric current runs through them when
monitor is operational. Change in electric field is used to find
the location. Only 75 per cent of light from the monitor is
transmitted.
Guidance for Children
133
Touch Screen Works – 2 of 2
 Three systems: [Contd …]
 Capacitive: When we touch, some of the charge is transferred
to the user, so the charge on capacitive layer decreases.
Measuring the decrease in circuits located at each corner of the
monitor helps finding the location. 90 per cent of the light from
the monitor is transmitted and so brighter than the Resistive
system.
 Surface Acoustic wave: Has two transducers (one receiving and
one sending) placed along x and y axes of the monitor’s glass
plate. Also placed on the glass are reflectors – they reflect an
electrical signal sent from one transducer to the other. 100 per
cent of light from the monitor is transmitted.
Guidance for Children
134
Sea Water Salty
 Most of the rivers and streams empty themselves into it.
The rivers are strewn with rock and plant debris. The
rocks contain many minerals and salts (especially
sodium chloride) which dissolve in the water. As the
rivers drain into the sea, a considerable amount of salt
gets dissolved in sea water.
 When these waters evaporate due to the heat of the
Sun, they leave the salt behind. The evaporated water
is brought back to the land in the form of rain and the
rivers carry the water again to the sea. As this cycle is
repeated, the amount of salt increases but the water
content remains the same.
Guidance for Children
135
People Sweat before Heavy Rain
 Sweating, also called perspiration, is a continuous
process. As the sweat glands, present below the skin
secrete sweat, it evaporates into the atmospheric air
depending on the humidity (moisture content) of the
air.
 If the air is dry (low humidity) the evaporation is fast.
But, before rain, the atmospheric air is saturated with
water vapour and so the evaporation of sweat slows
down. As a result with sweat accumulates on the skin
giving us a feeling that we sweat more.
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Condensed Milk & Fat
 Fat is an important constituent of milk. Cow’s milk should contain a
minimum fat of 3.5 per cent and buffallo’s milk 6 per cent. Actually the
fat content varies from breed to bread, and among individual animals.
 In Condensed milk, water is removed by evaporation in vacuum.
 Condensed milk is also prepared from skim milk (defatted milk) by
concentration again with or without sugar.
 Condensed milk prepared from full cream milk (fresh milk) contains the
same amount of fat present in ordinary milk. This is because by
concentration, only the volume of milk alone is reduced.
 Purpose of condense milk is to reduce the volume of milk to enable longdistance transport and improve shelf-life. In case of sweetened
condensed milk, the keeping quality is increased as the sugar prevents
the growth of micro-organisms by increasing the osmotic pressure
(osmoanabiosis) whereas in the unsweetened condensed milk, it is by
plasmolysis. Condensed milk can be diluted for use as fresh milk.
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Memory Effect & Battery Performance
 Memory effect is a term used to describe a self-conditioning phenomenon
by which nickel-cadmium cells tend to adjust their electrical properties
to a certain duty cycle to which they have subjected fro extended period
of time.
 Temporary loss in capacity is due to:
 Large number of unvarying partial discharge charge cycles.
 Extended storage without recharge or to extended periods with
insufficient charge.
 Prolonged constant current charging.
 Temporary loss in capacity means that the cells fails to deliver power if
an attempt is made to discharge them beyond the lower limit of the
repetitive discharge cycle.
 Complete discharge followed by recharge at not-too-low currents can
eliminate this effect. Another reason for temporary loss in capacity, and
often confused with memory effect, has to do with the formation of
alloys of nickel and cadmium under conditions of high temperature
overcharge.
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Finger Nails and Toe Nails
 Fingernails are made up primarily of dead cells, a horn-like
material called keratin. Growth takes place in the matrix, the
hidden part of the nail under the cuticle (the tissue that overlaps
with the visible part of the nail and rims the base of the nail). The
older cells die and harden as they are pushed out. The matrix also
includes the lunula, the whitish half-moon area at the base of the
nail. Fingernails grow about 0.1mm per day or 36mm a year, and
toenails grow at about 14mm a year.
 Finger nails and toe nails differ in growth. Possible reasons:
 Fingers nails are used more often and thus prone to injury and the
body needs to replenish any damaged nails fast.
 Nails grow faster when temperature is higher. Fingers are constantly
exposed but toe nails are mostly covered with shoes or slippers. Also,
they are more damp.
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Walking on Burning Coal
 People wet their feet abundantly before walking on
burning coal. When they start walking on the coal, this
moisture (may also be due to sweat) evaporates and
forms a protective gaseous layer beneath their feet.
 They walk on a protective layer of water vapour (which
has low heat capacity and poor thermal conduction)
rather than on the burning coal, as one would believe.
This is a short time effect and one should walk quickly
to avoid any further damage.
 Coal or wood embers, on which people generally walk,
have low heat capacity and poor thermal conduction. It
means coal being a bad conductor of heat will not pass
heat as efficiently as metals.
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