Transcript Document

18/07/2015
P1 Energy for the Home
(OCR)
AGAC
Heat and Temperature
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Heat is a type of energy that will flow from a warm area
to a colder one. For example…
cool down
This cup of coffee will ____
____
giving____
out heat
because it is _____
energy into the surroundings.
This drink (taken out of the
warm___
up because it
fridge) will _____
taking___
in heat energy from
is _____
the surroundings.
Words – giving out, warm up,
taking in, cool down
Specific Heat Capacity
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This can be thought of as “the capacity of an object to store
heat”. Consider some water:
If we heat this beaker up it’s fairly clear
that the amount of energy it gains
depends on how much water there is and
how hot it gets…
Energy = mass x s.h.c x temp rise
E = mcΔT
s.h.c = specific heat capacity
Each substance has a shc. The substances
with lower shc heat up faster
Temp/OC
150
100
50
Heating ice
This flat line shows where energy is being
used to push the particles further apart for
evaporation. The amount of energy needed
to turn 1kg of a liquid into a gas is called the
Specific Latent Heat of Vaporisation L.
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This diagonal line shows
where energy is being
used to increase the
temperature. The amount of
energy to increase the
temperature of 1Kg of water
By 100C is called the specific
heat capacity c
0
-50
This flat line shows where energy is being used
to break bonds – this has to be done during
melting. The amount of energy needed to turn
1kg of a solid into a liquid is called the Specific
Latent Heat of Fusion L.
Time/s
Latent Heat of Fusion
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From the previous slide we can say that the energy needed to
melt water is given by…
Energy = mass x specific latent heat of fusion
To work out L
experimentally you could…
Measure the amount
of energy needed to
melt 1Kg of ice
VIt = mL
A
12V
V
House insulation
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Loft insulation
Cavity wall
insulation
Double
glazing
Draught excluders
House insulation
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Type of insulation
Cost
Annual amount
saved
Loft insulation
£400
£80
Double Glazing
£2,000
£50
Cavity wall ins.
£600
£60
Draught excluder
£40
£20
1) Which type of insulation costs the most? Double glazing
2) Which type of insulation is the most effective? Loft insulation
3) Which type is the most “cost effective”? Draught excluder
4) Which type pays for itself after 40 years?
Double glazing
Efficiency
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Efficiency is a measure of how much USEFUL energy you
get out of an object from the energy you put INTO it.
For example, consider a TV:
Electrical
Energy (200J)
Sound (40J)
Efficiency = Useful energy out
Energy in
120 x100 = 60%
x100% = 200
Some examples of efficiency…
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1) 500J of electrical energy are put into a motor. The motor
converts this into 100J of movement energy. How
efficient is it?
100 x100 =20%
500
2) A laptop can convert 400J of electrical energy into 240J
of light and sound. What is its efficiency? Where does
the rest of the energy go?
240 x 100 = 60%
400
3) A steam engine is 50% efficient. If it delivers 20,000J of
movement energy how much chemical energy was put into
it?
40,000J
Conduction
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Conduction is all about when heat is transferred through a
solid The heat is passed on by ___________
vibrations in the
_____.
molecules. These vibrations get BIGGER when the solid has
heated
more ENERGY (i.e. when it is being _______).
better conductors than non-metals. This is
Metals are _______
electrons that can
because the heat is carried by free ________
carry the energy around the metal and give it to other
electrons and ions.
Words – vibrations, electrons, solid, heated, better
Convection
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Convection is all about when a gas or liquid
(“fluid”) moves and carries heat with it. When
expands This means
the fluid is heated it _________.
that it will become less ________
dense than the
colder fluid around it. Because of this the
float over the
warmer fluid will try to “_______”
colder fluid, and this is why warm air rises.
current This is
This is called a convection ________.
radiators
how heat reaches us from the ___________
in this room.
In CONDUCTION the heat was passed on
by VIBRATIONS in a SOLID
In CONVECTION the heat is passed on by
the FLUID expanding, rising and TAKING
THE HEAT with it
Words to use: expands, radiators, dense, heated, current, float
Some questions on convection…
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1) Freezers in supermarkets are often left open to the
air. Explain why the food does not melt easily.
Cold air does not rise – it falls
2) Explain why a hot air balloon rises in the air.
Heated air expands It becomes less dense
than the surrounding air
3) Explain why an ice cube floating at the top of a drink
will cool all of the drink.
Ice cube melts.
The cold water produced is more dense than the
surrounding drink and sinks
Radiation
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An introduction…
I’m cool!
I’m very hot!
White does
not absorb
as much heat- it
reflects it
Black
ABSORBS
More heat
Be careful, DO not use the word
“attract” heat
Some examples of radiation
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“Thermograms”
Some examples of radiation
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Radiation Practical
Time / min
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Temperature in each container / 0C
Black
Silver
1
90
90
2
81
85
3
73
81
4
66
77
5
60
73
6
55
70
7
51
66
8
48
63
9
46
60
10
45
58
Black cools
down quicker
than silver
Radiation
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Radiation is when heat moves around in electromagnetic _________
waves like
light does. Any hot object will emit heat radiation – the hotter it is, the
more radiation it emits. This type of radiation is called __________,
infra-red and
too much of it will cause _________.
sunburn Dark, matt colours will absorb AND
emit the _____
most infra-red radiation, and light, shiny colours will ________
reflect
it.
The main difference with radiation is that conduction and convection could
ONLY happen in solids, liquids or gases, whereas radiation will happen
space This is just as well, as otherwise we wouldn’t be
through an empty
_____ _____.
able to get any heat from the Sun
___.
Words – sun, reflect, infra-red, waves, most, empty space, sunburn
Anything HOT emits HEAT RADIATION – the hotter it
is, the more infra red radiation it emits
Understanding Heat Transfer
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1) Explain how and where all 3 processes
of heat transfer happen in a bonfire
2) By considering how a Thermos
Flask is built explain how it
manages to keep hot drinks hot
and cold drinks cold.
Understanding Heat Transfer 2
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3) Car radiators are
designed to help car
engines lose heat. Explain
how they do this.
4) Some houses have solar collectors on their roof. Explain
how they work:
Electromagnetic Radiation
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E-M radiation is basically a movement of energy in the form of
a wave. Some examples:
The Electromagnetic Spectrum
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Each type of radiation shown in the electromagnetic spectrum has a
different wavelength and a different frequency:
Low frequency, _____
long
(high) wavelength
High frequency,
short
_____ wavelength
Gamma
rays
X-rays
Ultra violet
Visible
light
Infra red
Microwaves
Radio/TV
γ
vacuum
Each of these types travels at the same speed through a _______
(300,000,000m/s), and different wavelengths are absorbed by different
black surfaces). This
surfaces (e.g. infra red is absorbed very well by _______
microwaves or
absorption may heat the material up (like infra red and ____________)
TV_______).
aerial
cause an alternating current (like in a __
Words – black, microwaves, long, short, TV aerial, vacuum
The Electromagnetic Spectrum
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Type of radiation
Uses
Dangers
Gamma rays
Treating cancer,
sterilisation
Cell mutation
X rays
Medical
Cell mutation
UVA, UVB and UVC
Sun beds
Skin cancer
Visible light
Seeing things
None (unless you
look at the sun)
Infra red
Remote controls,
heat transfer
Sunburn
Microwaves
Satellites, phones
Burns
TV/radio
Communications
Very few
Refraction through a glass block:
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Wave slows down and bends
towards the normal due to
entering a more dense medium
Wave slows down but is
not bent, due to entering
along the normal
Wave speeds up and bends
away from the normal due to
entering a less dense medium
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Refraction
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speed__
up or slow down due to
Refraction is when waves ____
travelling in a different _________.
A medium is
medium
something that waves will travel through.
Finding the Critical Angle…
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1) Ray gets refracted
3) Ray still gets refracted (just!)
THE CRITICAL
ANGLE
2) Ray still gets refracted
4) Ray gets
internally reflected
Uses of Total Internal Reflection
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Optical fibres:
An optical fibre is a long, thin, transparent
_______ rod made of
glass or plastic. Light is _______
internally reflected from one
large
end to the other, making it possible to send ____
chunks of information
Optical fibres can be used forcommunications
_________ by sending
electrical signals through the cable. The main advantage
signal loss.
of this is a reduced ______
Words – communications, internally, large, transparent, signal
Analogue vs. Digital
Analogue signals (like talking or
music) continually vary in
amplitude and/or frequency
1
0
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+
Digital signals, however, are either
off or on, and the information is sent
in a series of pulses
There are two main advantages of digital:
1) More information can be sent down the same cable
2) Better quality, because a digital signal can be amplified without
amplifying the extra noise:
Wireless devices
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The trouble with optical fibres and electrical connections is
that they need wires. This is a big advantage when sending
information using radio waves and microwaves. However, they
have disadvantages as well...
Blocking reception
Microwaves can be blocked
by obstructions
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Using Satellites with microwaves
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Microwaves
are used to
communicate
with satellites
Using Radio waves
Radio waves are reflected off the
ionosphere (an electrically charged
layer in the atmosphere)
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Diffracting Radio Waves
A low frequency radio wave can be
diffracted over obstacles but some
signal strength will be lost.
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Some definitions…
1) Amplitude – this is
“how high” the wave is:
2) Wavelength () – this is the
distance between two
corresponding points on the
wave and is measured in metres:
3) Frequency – this is how many waves pass by
every second and is measured in Hertz (Hz)
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Some definitions…
Transverse waves
are when the
displacement is at
right angles to
the direction of
the wave…
Longitudinal waves
are when the
displacement is
parallel to the
direction of the wave…
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The Wave Equation
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The wave equation relates the speed of the wave to its
frequency and wavelength:
Wave speed (v) = frequency (f) x wavelength ()
in m/s
in Hz
in m
V
f

Some example wave equation questions
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1) A water wave has a frequency of 2Hz and a wavelength
of 0.3m. How fast is it moving?
0.6m/s
2) A water wave travels through a pond with a speed of
1m/s and a frequency of 5Hz. What is the wavelength
of the waves?
0.2m
3) The speed of sound is 330m/s (in air). When Dave
hears this sound his ear vibrates 660 times a second.
What was the wavelength of the sound?
0.5m
4) Purple light has a wavelength of around 6x10-7m and a
frequency of 5x1014Hz. What is the speed of purple
light?
3x108m/s
Lasers
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Lasers produce light waves that are “coherent” – i.e. they have
the same frequency and they are in phase:
These two waves have
different amplitudes but
the same frequency and hit
their peaks at the same
time – they are “in phase”
These two waves start
opposite to each other –
they are “in antiphase”
Using lasers in CDs
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This is a magnified
image of the CD surface
The Structure of the Earth
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A thin crust 10-100km thick
A mantle – has the
properties of a solid
but it can also flow
A core – made of
molten nickel and iron.
Outer part is liquid
and inner part is solid
How do we know this? These facts have all been
discovered by examining seismic waves (earthquakes)
Seismic waves
Earthquakes travel as waves through the Earth – we call them
SEISMIC WAVES. There are two types:
P waves:
1) They are longitudinal so they cause the ground
to move up and down
2) They can pass through solids and liquids
3) They go faster through more dense material
S waves:
1) They are transverse so they cause the ground
to move from right to left
2) They ONLY pass through solids
3) They are slower than P waves
4) They go faster through more dense material
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P and S waves
A quick way to remember the difference:
S waves are tranSverse
P waves are the other type-longitudinal
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Seismic waves
S waves will only travel
through a solid
crust
Outer
core
mantle
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Inner
core
P waves travel through
the Earth and are
refracted when they
pass through a medium
The paths of these
waves are all curved
because density is
gradually changing
These observations tell us 3 things about the Earth: 1) It has a thin
crust, 2) it has a semi-fluid mantle where density increases with depth,
3) a core with a liquid outer part and a solid inner part.
Suncream
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Ultra violet radiation in sunshine can be dangerous and cause
skin cancer:
It is recommended that you spend no more than 20
minutes in the sun on a sunny day. However, you
could also use suncream:
Safe time = exposure time (e.g. 20 mins) x sun protection factor
Global Warming
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Facts:
1) The 10 warmest years
of the last century
have all occurred
within the last 15
years
2) Sea level has risen by
between 12 and 24cm
in the last 100 years
3) Rainfall has risen by
1%
Ozone
Diagram showing the quantity
of ozone in different parts of
the southern hemisphere
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Global production of CFCs
over the last 60 years