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69 Cards in this Set
- Front
- Back
What kind of current do photocells produce? What does this mean? |
A direct current - the current flows the same way round the circuit all the time |
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What are photocells made of?
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Silicon (a semi-conductor)
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What happens when sunlight falls on the cell? (2 points)
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- The silicon atoms absorb some of the energy, knocking loose some electrons
- These electrons then flow around the circuit = electricity |
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What 3 things does the current and power output of a photocell depend on?
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- Surface area
- The intensity of the light - The distance from the light |
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What are 6 advantages of photocells?
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Sturdy
Low maintenance Last a long time No power cables or fuel Renewable Doesn't pollute environment |
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What is a major disadvantage of photocells?
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No sunlight = no power
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What are curved mirrors used for?
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To focus the Sun's light and heat
Single curved mirror = eg. solar oven Large curved mirror = generate steam to produce elec |
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How do you make devices that collect energy from the Sun most efficient?
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Most efficient if they track the Sun's movement across the sky
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When can energy collectors capture the maximum amount of light and heat?
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When they are pointed directly at the Sun
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What is passive solar heating?
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Involves any system that can capture the Sun's energy directly eg. greenhouse
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How do solar water heaters work?
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Glass lets in heat and light from the sun and is absorbed by the black pipes to heat the water
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How does a greenhouse work? (5 points)
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1) The sun produces radiation with a very short wavelength
2) Transparent glass allows heat and light through 3) The ground and plants absorb radiation and heat up 4) They re-radiate the infrared but because they are much cooler than the sun = longer wavelength 5) Won't pass through and is reflected back |
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How is wind produced?
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Energy from the sun heats up the atmosphere which causes convection currents
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How do wind turbines generate electricity?
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Wind turbines convert kinetic energy of moving air into electricity. The wind turns the blades = turn a generator
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What are 4 advantages of wind-turbines?
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Renewable energy source
Robust Cheap to run No pollution |
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What are 5 disadvantages of wind-turbines?
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Unreliable (depends on the wind speed)
Eye sore Space required Considered noisy Expensive to set up |
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What is the National Grid?
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The network of pylons and cables which cover the whole country, taking electricity from power stations to homes and industry
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What are the 3 stages of how energy is converted to electricity in power stations?
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1. BOILER: Fuel produces heat to genetate steam
2. TURBINE: The moving steam turns the turbine 3. GENERATOR: Rotating movement from turbine is converted to electricity by electromagnetic induction |
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What is electromagnetic induction?
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Creation of voltage (maybe current) in a wire which is experiencing a change in magnetic field
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Why do generators produce an alternating current (AC)?
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1. Generators rotate a coil in a magnetic field
2. Every 1/2 turn, the current in coil swaps direction |
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What happens if you turn a coil in a magnetic field faster?
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Higher voltage and current
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What is the dynamo effect?
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Using electromagnetic induction to transform kinetic energy into electrical energy
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What are the 2 different situations where you get electromagnetic induction?
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1) An electrical conductor moves through a magnetic field
2) The magnetic field through an electrical conductor changes |
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What happens if the direction of movement is reversed in a magnetic field?
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The voltage/current is reversed to
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What 3 things can you increase to get a bigger voltage/current?
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1) Strength of magnet
2) No. of turns in coil 3) Speed of movement |
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What are two advantages of burning fossil fuels for energy?
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Readily available at the moment
Concentrated source of energy (a little fuel gives a lot of energy) |
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What are four disadvantages of burning fossil fuels for energy?
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Produces acid rain and carbon dioxide
We have no control of the price or supply as we buy it from other countries Non-renewable |
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What are four advantages of biomass?
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Renewable
Quickly make more "carbon neutral process" = produces CO2 when burnt but plants take in this CO2 Doesn't need to be imported |
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What are two disadvantages of biomass?
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Need a lot of space
Needs a lot to produce energy |
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What do you need to transmit lots of electrical power?
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High voltage OR current
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Why can a high current be inefficient?
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Because the cables get hot (heat wasted)
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What happens to the voltage before the electricity is sent round the country? Why?
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The voltage is transformed to 400,000V
This keeps the current low so less energy is wasted by heating cables |
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How do you increase the voltage?
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A step up transformer
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How do you bring voltage down to safe usable levels?
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A step down trnasformer
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Why is mains electricity an alternating current (AC)?
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Transformers only work on AC
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What is the equation for total energy input?
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Total energy input = useful energy output + waste energy output
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What is the equation for efficiency?
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Efficiency = Useful energy output / total energy input (x100)
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What is power?
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A measure of the rate at which energy is used
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What is the equation for power?
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Power (W) = Voltage (V) x Current (A)
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What is the equation for the energy supplied (in kWh)
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Energy supplied = Power x time
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How do you work out the cost of energy?
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Cost = number of units x price per unit
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What are two advantages of off-peak electricity?
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Cheaper for the consumer
Cost effective for the electricity company as the power stations cannot be turned off at night |
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What are two disadvantages of off-peak electricity?
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Risk of fire if no one is watching appliances over night
People start to fit their routine around off peak rates |
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What do the gases in the atmosphere do with radiation? How do they do this?
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They filter out certain types of radiation from the sun by absorbing or reflecting radiation of certain wavelengths (infrared)
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How does the greenhouse effect help regulate Earth's temperature? (5 points)
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1) Earth absorbs short wavelength EM radiation from the sun. This warms the earth and the eart emits some of this EM radiation back
2) Most that is emitted back is longer wavelength infrared radiation (heat) 3) A lot of this is absorbed by atmospheric gases like carbon dioxide, methane and water vapour 4) The gases re-radiate heat in all directions 5) Atmosphere = insulating layer = stops earth losing heat at night |
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Give three things that are increasing carbon dioxide levels
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1)People use more energy (cars) = releases CO(2)
2)More land is needed for houses and food = trees chopped down and burnt = less CO(2) absorbed, more released 3)Natural sources like respiration and volcanic eruptions |
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Give three things that are increasing methan levels
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1) Cattle farming increased = more methane
2) Decaying waste in landfill 3) Naturally = volcanoes and animals |
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Give two things that are increasing water vapour levels
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1) Natural sources like oceans
2) Power stations |
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Why is the climate changing?
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More fossil fuels are being burnt and so the level of carbon dioxide has increased. The global temperature has a link between the concentration of CO(2).
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What can we expect from changes in the weather?
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1) Many regions suffer more extreme weather
2) Increased number of hurricanes 3) Affects food production = regions too dry/wet to grow |
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What are 2 human causes of temperature change?
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1) The rising CO(2) level
2) Soot and gases from factories can reflect heat from cities = increases local temperatures |
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What are 2 natural causes of temperature change?
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1) Ash and gases thrown into the atmosphere by volcanoes can reflect radiation from the Sun back into space = cools earth down
2) Changes in our orbit around the sun can cause ice ages |
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When is nuclear radiation given off?
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When an unstable nucleus decays
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Give properties of alpha particles on:
1) Size and movement 2) Penetration 3) Ionisation |
1) Relatively big, heavy and slow moving (2 protons and 2 neutrons)
2) Stopped quickly and don't penetrate far into materials 3) Strongly ionising |
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Give properties of beta particles on:
1) Size and movement 2) Penetration 3) Ionisation |
1) They're electrons = small and move fast
2) Penetrate moderately 3) Moderately ionising |
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Give properties of gamma particles on
1) Size and movement 2) Penetration 3) Ionisation |
1) No mass
2) Penetrate a long way into materials 3) Weakly ioning |
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What can a) alpha b) beta and c) gamma be stopped by?
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a) Skin or paper
b) A few mm of aluminium c) A few cm of lead |
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How can you identify the type of radiation?
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By it's penetrating power
Place paper, aluminium and lead between the source and a detector and see if the radiation is detected |
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What is a use of alpha radiation?
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Smoke detectors
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How do smoke detectors work? (3 points)
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1)The smoke detectors have a weak source of alpha radiation close to two electrodes
2)The radiation ionises the air and a current flows between the electrodes 3) If there's a fire the smoke absorbs the radiation - the current stops - alarm sounds |
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What is are two uses of beta radiation?
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Tracers and thickness gauges
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How is beta used as a tracer?
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Radioactive source injected in to the body
A radiation detector is used to follow its progress to see if the body is working properly |
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How is beta used as in thickness gauges?
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1) The radiation source is placed above a detector with the paper in-between
2) If the paper is too thick = beta detected decreases and makes rollers pinch up 3) If the paper is too thin = beta reading increases and makes rollers open a bit |
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Why are gamma and beta used as tracers in the body?
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They are able to pass out of the body
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What two uses does gamma radiation have?
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1) Cancer treatment
2) Sterilise medical equipment |
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How is gamma used to treat cancer?
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1) High doses kill all living cells
2) Directed carefully at the cancer at the correct dosage to kill the cancerous cells without damaging too many normal cells |
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How is gamma used to sterilise medical equipment
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Kills all the microbes
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What are 4 advantages of nuclear power?
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- Lots of energy without releasing CO(2)
- Release lots more energy than chemical reactions (eg. burning) - Nuclear fuel = cheap - Plenty of uranium in the ground |
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What are 5 disadvantages of nuclear power?
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- Power stations = expensive to build
- Processing uranium before use = expensive - Risk of leak or major catastrophe - Radioactive waste produced = dangerous and difficult to dispose of - Uranium = non-renewable |