Transcript Biology revision
P1 - Universal physics
27 April 2020 A Massawe 1
How science works
• • • • • Independent variable –
change
this is the quantity that
you
Dependent variable this is what
you measure
Control variable – this is what must be
kept the same
to ensure a
fair test
Hypothesis – an idea based on observations without experimental evidence Secondary evidence data collected by someone else, you may find it in a book or on the internet 27 April 2020 A Massawe 2
How do scientist validate results?
1. they repeat experiment results 2. they publish their findings in scientific journals 3. conference presentation 4. peer review/other scientists investigate the same findings.
27 April 2020 A Massawe 3
Models of the solar system
• Geocentric model(Ptolemy) the earth at the centre and all the planets and the sun orbiting around it • Heliocentric model(Nicolaus Copernicus) - the sun at the centre of the universe, based on observations with the
telescope
27 April 2020 A Massawe 4
Observing the universe
• Optical telescopes light from space observe visible • The Hubble telescope is an optical telescope in space • Optical telescopes on the ground have some disadvantages: 1. they can only be used at night 2. they cannot be used if the weather is poor or cloudy.
27 April 2020 A Massawe 5
Observing the universe
• Many objects in space do not give out visible light but give out other types of energy-carrying waves like radio waves and microwaves • The Planck space telescope detects microwaves 27 April 2020 A Massawe 6
Observing the universe
•
Radio telescopes
detect radio waves coming from space, they are usually very large and expensive.
• Advantage over optical telescopes – 1. can be used in bad weather because the radio waves are not blocked by clouds as they pass through the atmosphere. 2. can also be used in the daytime as well as at night.
27 April 2020 A Massawe 7
Telescopes
• • • focus the light. Parallel light rays entering a convex lens come out and pass through at a point known as the
focal point
27 April 2020 A Massawe 8
Investigating converging lenses
• A Converging lens can be used to produce a magnified image.
The amount of magnification depends on: 1. How curved the surface of the lens is 2.
How far the object is from the lens Two types of image can be seen. 1. A
real image
Is the image formed where the light rays are focused. 2. A
virtual image
is one from which the light rays appear to come, but don’t actually come from that image like in a plane (flat) mirror.
27 April 2020 A Massawe 9
Investigating converging lenses
•
Object more than two focal lengths from the lens
image is inverted, smaller, appear between 1 and 2 focal lengths, real image 27 April 2020 A Massawe 10
Investigating converging lenses
•
Two focal lengths in front
image is inverted, same size, appears at 2 focal lengths, real image 27 April 2020 A Massawe 11
Investigating converging lenses
•
Between one and two focal lengths
image is inverted, made bigger, appear beyond 2 focal lengths, real image 27 April 2020 A Massawe 12
Investigating converging lenses
•
One focal length
no image is formed 27 April 2020 A Massawe 13
Investigating converging lenses
•
Object is less than one focal length from the lens.
image right way up, image made bigger, virtual image 27 April 2020 A Massawe 14
Refracting telescopes
• A refracting telescope works by bending light through a lens so that it forms an image • Problems with refracting telescopes: 1.
some of the light reflects off the lens so the image is very faint 2. the size of the lens is limited 15 27 April 2020 A Massawe
Reflecting telescopes
• • In a reflecting telescope the image is formed by reflection from a curved mirror It is then magnified by a Convex lens (the eyepiece) 27 April 2020 A Massawe 16
Compare and contrast lenses and mirrors
Similarities
1. A convex lens acts a lot like a concave mirror. Both converge parallel rays to a focal point, and form images with similar characteristics.
2. A concave lens acts a lot like a convex mirror. Both diverge parallel rays away from a focal point, and form only virtual, smaller images.
27 April 2020 A Massawe 17
Compare and contrast lenses and mirrors
Differences
1. Light reflects from a mirror. Light goes through, and is refracted by, a lens (with some light being reflected off the lens).
2. Lenses have two focal points, one on either side of the lens.
3. A concave mirror converges parallel light rays to a focal point. For lenses, parallel rays converge to a point for a convex lens. A convex mirror diverges light, as does a concave lens.
27 April 2020 A Massawe 18
Refraction in different materials
T owards (normal) A ir G lass A way (from normal) G lass A ir 27 April 2020 Remember the word: TAGAGA A Massawe 19
Effects of refraction
27 April 2020 A Massawe 20
Effects of refraction
27 April 2020 A Massawe 21
What are waves?
• to place without matter (solid, liquid or gas) being transferred, e.g. Mexican wave in a football crowd Waves travel through medium sound waves seismic waves No medium required visible light infrared rays microwaves other types of electromagnetic radiation 27 April 2020 A Massawe 22
Transverse or longitudinal waves?
Transverse waves Longitudinal waves the vibrations are at right angles to the direction of travel e.g.
- light, - electromagnetic radiation, - water waves, - S waves (a type of seismic wave) the vibrations are along the parallel to the direction of travel e.g. - sound, - P waves (a type of seismic wave) 27 April 2020 A Massawe 23
• •
What are waves?
wavelength
is the distance between a point on one wave and the same point on the next wave The is the maximum distance of the particles in a wave from their normal positions • The of a wave is the number of waves produced by a source each second.
27 April 2020 A Massawe 24
How fast do waves travel?
• wave speed (m/s) = frequency (Hz) × wavelength (m) wave speed frequency wavelength 27 April 2020 A Massawe 25
Reflection
• Sound waves and light waves
reflect
The angle of incidence equals the from surfaces. angle of reflection • • Smooth surfaces produce strong
echoes
waves hit them Rough surfaces
scatter
when sound sound and light in all directions 27 April 2020 A Massawe 26
• •
Refraction
Sound waves and light waves
change speed
when they pass across the boundary between two substances with different densities, e.g. air and glass. This causes them to change direction and this effect is called
refraction
• There is no change in direction if the waves cross the boundary at an angle of
90°
- in that case they carry straight on (although there is still a change in speed).
27 April 2020 A Massawe 27
Electromagnetic spectrum
Wavelength ( ) increases Frequency (
f
) increases
Gamma X-ray Ultra violet
Short wavelength High energy Most penetrating 27 April 2020
Light Infra-red
Least penetrating A Massawe
Microwaves Radio
Long wavelength Low energy Least penetrating 28
Hazards of electromagnetic radiation
Microwaves Infrared radiation X rays Gamma rays cause internal heating of body tissues is felt as heat and causes skin burns damage cells, causing mutations (which may lead to cancer) and cell death also damage cells, causing mutations (which may lead to cancer) and cell death.
27 April 2020 A Massawe 29
The three main types of ultraviolet radiation, and some of their effects
Type
UV C UV B UV A
frequency hazard
high causes severe damage to cells, skin cancer medium causes severe sunburn and damage to cells low weaker effects than UV B 27 April 2020 A Massawe 30
Uses of electromagnetic radiation
• •
Radiowaves
– broadcasting, communications & satellite transmissions
Microwaves
– cooking, communications & satellite transmissions • •
Infrared
- cooking, thermal imaging, short range communications, optical fibres, TV remote controls & security systems
Visible light
illumination – vision, photography & A Massawe 31 27 April 2020
Uses of electromagnetic radiation
•
Ultraviolet
– security marking, fluorescent lamps, detecting forged bank notes & disinfecting water •
X-rays
- observing the internal structure of objects, airport security scanners & medical X-rays •
Gamma
- sterilising food and medical equipments, detection of cancer and its treatment 27 April 2020 A Massawe 32
Exam tip
• To make your answer as full as possible you should include: 1. the advantages and disadvantages of each type of radiation 2. clearly indicate the precise use and why 3. include information about frequency and wavelength 27 April 2020 A Massawe 33
Ionising radiation
• Alpha, beta and gamma are ionising radiation: they can knock electrons out of atoms and form charged particles • Radiation can be harmful, but it can also be useful - the uses of radiation include to: 1. detect smoke 2. gauge the thickness of paper 3. treat cancer 4. sterilise medical equipment.
27 April 2020 A Massawe 34
Types of radiation
• Nuclear radiation comes from the nucleus of an atom of substances which are
radioactive
• All radiation transfers energy. There are three types of nuclear radiation:
alpha, beta and gamma
alpha beta gamma
27 April 2020 A Massawe 35
The solar system
• The solar system consists of: 1. a star - the Sun 2. satellites - moons - in orbit around most of the planets 3. comets and asteroids in orbit around the Sun.
4. eight planets, including the Earth, and smaller dwarf planets, such as Pluto, Ceres and Eris.
27 April 2020 A Massawe 36
Space exploration
• The Search for Extra-Terrestrial Intelligence (SETI) is a programme that uses to look for non-natural signals coming from space •
Space probes
photograph planets looking for evidence of life •
Space landers
touch down on planets and take a soil sample, which is analysed for evidence of life.
A Massawe 37 27 April 2020
What is a spectrometer?
• Spectrometer is an instrument that can split up light to show the colours of the spectrum 27 April 2020 A Massawe 38
The origins of the Universe
• Scientists believe that the universe began in a hot 'big bang' about 13 billion years ago • Two evidences of the Big Bang Theory are; 1. the existence of a microwave background radiation, 2. red-shift.
27 April 2020 A Massawe 39
Other theories for the origin of the universe
• one of many - some that have existed in the past, and others that will exist in the future • When the universe contracts in a Big Crunch, a new universe is created in a new Big Bang.
• expands new matter is created, so that the overall appearance of the universe never changes.
27 April 2020 A Massawe 40
Life cycle of a star
27 April 2020 A Massawe 41
The future of other stars
• weight star will still become a red giant, but then: 1. it blows apart in a huge explosion called a supernova 2. the central part left behind forms a neutron star, or even a black hole, if it is heavy enough 3. black holes have a large mass, and a large gravity - even light cannot escape them because their gravitational field is so strong 27 April 2020 A Massawe A supernova is an exploding star 42
Evidence for the Big Bang Theory
• Red-shift - red is a longer wavelength of light, this means that the galaxies must all be moving away from us • •
Cosmic Microwave Background radiation -
electromagnetic radiation which was present shortly after the big bang is now observed as background microwave radiation.
A satellite called COBE mapped the background microwave radiation of the universe 27 April 2020 A Massawe 43
Evidence for the Big Bang Theory
Evidence Interpretation
The light from other galaxies is red shifted.
The other galaxies are moving away from us. This evidence can be used to explain both the Big Bang theory and Steady State universe.
The further away the galaxy, the more its light is red shifted.
The most likely explanation is that the whole universe is expanding. This supports the theory that the start of the universe could have been from a single explosion.
Cosmic Microwave Background (CMB) The relatively uniform background radiation is the remains of energy created just after the Big Bang.
27 April 2020 A Massawe 44
Doppler effect for a moving sound source
Long wavelength Low frequency Short wavelength High frequency 27 April 2020 A Massawe 45
Ultrasound and infrasound
• through a medium •
Ultrasound waves
have a frequency above the normal range of human hearing - they can be used to 1. scan for birth defects in unborn babies 2. scan for defects in manufactured equipment.
•
Infrasound
has a frequency below normal hearing can be used to 1. track animals 2. monitor seismic activity 27 April 2020 A Massawe 46
•
Sound waves
When an object vibrates, it produces sound. The bigger the vibrations, the greater the amplitude and the louder the sound • • • 1 and 2 - two sounds with the same frequency but different amplitude. Sound 1 (smaller amplitude) is quieter than sound 2.
2 and 3 - two sounds with the same amplitude but different frequencies. The faster the vibrations, the higher the frequency and the more highly pitched the sound.
So sounds 2 and 3 have the same volume (loudness), but 3 (higher frequency) is higher pitched.
27 April 2020 A Massawe 47
Ultrasound
• • When ultrasound waves reach a boundary between two substances with different densities, they are partly reflected back and detected e.g. sound travels through water at about 1,400 m/s. If it takes 0.5 s for a sound to reach a boundary and reflect back to the detector, the total distance travelled is: distance = speed × time = 1,400 × 0.50
= 700m 27 April 2020 A Massawe 48
27 April 2020
Sonar
• • • • Sonar is used on ships and submarines to detect fish or the sea bed. A pulse of ultrasound is sent out from the ship. It bounces off the seabed or shoal of fish and the echo is detected. The time taken for the wave to travel indicates the depth of the seabed or shoal of fish A Massawe 49
Infrasound
• • • Infrasound has frequency less than 20Hz, this is below the range that humans can hear (20-20,000Hz). Infrasound is detected using a microphone.
Three uses of infrasound: 1. to detect volcanic eruptions - as a volcano erupts it produces infrasound, which can be detected even if the volcano is in a remote location far away 2. to track the passage of meteors through the atmosphere 3. to track animals (elephats use infrasound to communicate) even if they are hidden in dense forests. This helps with the conservation and protection of these animals.
27 April 2020 A Massawe 50
•
Seismic waves
The crust and upper mantle are broken into large • • These plates move slowly, but can cause
earthquakes
and
volcanes
where they meet. The seismic waves produced by an earthquake are monitored and tracked.
- liquid nickel and iron - Solid nickel and iron 27 April 2020 A Massawe 51
• •
Seismic waves
Earthquakes happen when large parts of the Earth's crust and upper mantle move suddenly Earthquakes produce shockwaves called seismic waves. These waves can be detected using seismographs.
type of wave relative speed can travel through P waves
longitudinal faster solids and liquids
S waves
transverse slower solids only 27 April 2020 A Massawe 52
Difference between S and P waves
•
S-waves
- transverse - slow moving - travel through solids only •
P-waves
- longitudinal - fast moving - travel through liquids and solids only A Massawe 53 27 April 2020
Producing electricity
• • An electric current can be produced by moving a magnet inside a coil of wire attached to a sensitive ammeter, the needle is seen to move. to move around the circuit as a
current
54 27 April 2020 A Massawe
27 April 2020
Producing electricity
• • Here the magnet is being pushed into the coil. The ammeter shows current induced in a positive direction.
• • Now the magnet is stationary inside the coil. There is no current being produced in the coil, shown by the zero reading on the ammeter • The magnet is being pulled out. The ammeter shows current being induced in the opposite direction to before.
A Massawe 55
Producing electricity
• The size of this induced current can be increased by 1. move the magnet faster 2. use a stronger magnet 3. increase the number of turns on the coil 4. increase the area of the coil.
56 27 April 2020 A Massawe
27 April 2020
Direct and alternative current
• • • Direct current – DC, current flows in only one direction . Batteries and solar cells supply DC electricity. The diagram shows an oscilloscope screen displaying the signal from a DC supply.
• • • Alternating current – AC, current constantly changes direction. Mains electricity is an AC supply. The UK mains supply is about 230V. It has a frequency of 50Hz, which means that it changes direction and back again 50 times a second. A Massawe 57
Producing electricity
• Generators (bicycle dynamo) induce a current by spinning a magnet inside a coil of wire • When this happens, a potential difference - voltage - is produced between the ends of the coil, which causes a current to flow.
27 April 2020 • As the bicycle moves, the wheel turns a magnet inside a coil • This induces enough electricity to run the bicycle's lights • The faster the bicycle moves, the greater the induced current and the brighter the lights.
A Massawe 58
•
Large-scale electricity production
Turning generators indirectly - generators can be turned indirectly using fossil or nuclear fuels 1. Heat is released from fuel and boils the water to make steam. 2. The steam turns the turbine. 3. The turbine turns a generator and electricity is produced.
4. The electricity goes to the transformers to produce the correct voltage A Massawe 59
Different sources of energy
• • • • • • Renewable energy resources include: wind energy tidal waves hydroelectric power geothermal energy solar energy biomass energy, for example energy released from wood 27 April 2020 A Massawe 60
Solar cells or Solar energy
• Solar cells (or photocells) turn light energy from the Sun directly into direct current electricity. Advantages Its renewable No maintenance No power lines required No fuel Long lifetime No green house gases Disadvantages Expensive to build Low efficiency – requires large area Manufacture causes pollution Low power output 27 April 2020 A Massawe 61
Hydroelectricity
• A dam is built to trap water, usually in a valley where there is an existing lake.
• Water is allowed to flow through tunnels in the dam, to turn turbines and thus drive generators.
Advantages Disadvantages No waste or pollution Very reliable Low running cost Quick start-up time Electricity can be generated constantly Requires hilly areas Destroys habitats Expensive to build 27 April 2020 A Massawe 62
Wind turbines
• Wind turbines (or aero-generators) use large blades to capture the kinetic energy of the wind. • This kinetic energy is used to directly turn a turbine and produce electricity.
Advantages Disadvantages No waste or greenhouse gases No fuel is needed Can be tourist attractions Noisy May spoil views Kill birds The amount of electricity generated depends on the strength of the wind.
27 April 2020 A Massawe 63
Geothermal energy
• Hot rocks underground heat water to produce steam.
• Holes are drilled down to the hot region, steam comes up to drive turbines, which drive electric generators Advantages No pollution No fuel is needed Easy and cheap to run Disadvantages Hot rocks are not available everywhere Geothermal site can run out of steam Hazardous gases or minerals may come up 27 April 2020 A Massawe 64
Tidal power
• These work rather like a hydro-electric scheme, except that the dam is much bigger.
Advantages High power output Reliable power source Long lifetime Low running costs No fuel needed Tides are predictable Not expensive to maintain Disadvantages Tidal range varies Destroys habitats Expensive to build 27 April 2020 A Massawe 65
Biomass
• Wood is burnt to heat our homes and cook our food. • Sugar cane can be fermented to make alcohol, which can be burned to generate power.
Advantages The fuel is cheap Less demand on the fossil fuel Disadvantages Difficult to collect or grow large quantities It produce greenhouse gases 27 April 2020 A Massawe 66
Transformers
• Transformers are used in the National Grid to
reduce energy losses
from the wires during transmission.
• A transformer that increases the voltage is called a
step-up transformer
• A transformer that decreases the voltage is called a
step-down transformer
e.g. adapters and rechargers for mobile phones and CD players.
27 April 2020 A Massawe 67
• •
Transformers
The ratio between the voltages in the coils is the same as the ratio of the number of turns in the coils primary voltage = turns on primary secondary voltage turns on secondary This can also be written as: Vp / Vs = Np / Ns • • Step-up transformers have
more
secondary coil than primary coil.
turns on the Step-down transformers have
fewer
secondary coil than the primary coil.
turns on the 27 April 2020 A Massawe 68
•
Transformers
A transformer has 20 turns on the primary and 400 on the secondary. What is the output voltage if the input voltage is 500V?
Vp / Vs = Np / Ns Therefore Vs / Vp = Ns / Np Vs / 500 = 400 / 20 Vs = 500 x ( 400 / 20 ) Vs= 10,000 Volts 27 April 2020 A Massawe 69
•
Current
A current flows when an electric charge moves around a circuit – measured as the rate of flow of charge • The current flowing through a component in a circuit is measured using an
ammeter
• The units for current is
amperes or A
27 April 2020 A Massawe 70
•
Potential difference (voltage)
A potential difference, also called voltage, across an electrical component is needed to make a current flow through it.
• Potential difference across a component in a circuit is measured using a
voltmeter
• The voltmeter must be connected in
parallel
component.
with the 27 April 2020 A Massawe 71
•
Power, current and potential
Power
transferred.
difference
is a measure of how quickly energy is • You can work out power using this equation: power (W) = voltage (V) × current (A) power voltage current A Massawe 27 April 2020 72
Power and energy
• • Power is a measure of how quickly energy is transferred. You can work out power using this equation: energy transformed power time A Massawe 27 April 2020 73
• •
Paying for electricity
The amount of electrical energy transferred to an appliance depends on its power, and on the length of time it is switched on for The amount of mains electrical energy transferred is measured in kilowatt-hours (kWh). One unit is 1kWh energy transferred (kWh) = power (kW) × time (h) • The cost of the electricity used is calculated using this equation: cost = power (kW) × time (hour) × cost of 1 kWh (pence) 27 April 2020 A Massawe 74
Saving energy (cost efficiency)
payback time = cost of energy-saving measure ÷ money saved each year • e.g. Double-glazing might cost £2,500 and save £100 a year. What is the payback time?
= 2,500 ÷ 100 = 25 years 27 April 2020 A Massawe 75
•
Saving energy (cost efficiency)
When buying an energy-saving device, it is important to consider the advantages and disadvantages.
• Some disadvantages would be: 1. initial cost 2. use of extra resources to manufacture new device 3. cost of disposal of old device.
• Some of the advantages would be: 1. cost efficiency 2. saving energy and resources.
27 April 2020 A Massawe 76
•
Energy transfer and efficiency
Forms of energy -
E
nergy
N
ames
M
ost
K
ids
H
ate
L
earning
GCSE
• Magnetic - energy in magnets and electromagnets • Kinetic - the energy in moving objects. Also called movement energy • Heat – also called thermal A Massawe 27 April 2020 77
Energy transfer and efficiency
• Light – also called radiant energy 27 April 2020 • Gravitational potential – stored energy in raised objects • Chemical – stored energy in fuel, foods and batteries • Sound – energy released by vabrating objects A Massawe 78
27 April 2020
Energy transfer and efficiency
• Electrical – energy in moving or static electric charges • Elastic potential – stored energy in stretched or squashed objects • Nuclear – stored in the nuclei of atoms A Massawe 79
•
Energy transfers
Different types of energy can be transferred from one type to another, e.g. of useful energy transfer 27 April 2020 A Massawe 80
• •
Sankey diagrams
Sankey diagrams summarise all the energy transfers taking place in a process. The thicker the line or arrow, the greater the amount of energy involved.
27 April 2020 A Massawe 81
• • • •
Calculating efficiency
The efficiency of a device such as a lamp can be calculated using this equation: efficiency = useful energy transferred x 100 energy supplied The efficiency of the filament lamp is (10 ÷ 100) × 100 = 10% - this means that 10% of the electrical energy supplied is transferred as light energy (90% is transferred as heat energy).
The efficiency of the energy-saving lamp is (75 ÷ 100) × 100 = 75% - this means that 75% of the electrical energy supplied is transferred as light energy (25% is transferred as heat energy).
27 April 2020 A Massawe 82