P2 Physics
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- Created by: Lydia1
- Created on: 04-01-13 18:21
What are photocells?
They are a device that generates electricity directly from sunlight. They generate a direct current(like a battery)
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What does direct current mean?
The current flows the same way around the circuit all the time unlike AC current which changes direction all the time(like the mains in your home)
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How do the photocells generate the electricity?
The photocells are made of silicon so when the sunlight falls onto the cell, the silicon atoms absorb some energy which knocks loose some electrons which then flow round in a circuit and this is the electricity.
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What factors affect the amount of current produced?
The surface area of the photocell, Intensity of the light and distance from the light.
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Give an advantage and disadvantage of a photocell
advantage, they are sturdy/low maintenance and you dont need cables-----disadv, if there is no sunlight, there is no power
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What do curved mirrors do?
they focus the suns light and heat onto a device that is used to change that light and heat into electricity.
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Wat is Passive Solar Heating?
When the suns energy is used to heat something directly.
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How can a house or building use passive solar heating?
Heat/light from the sun is absorbed by objects in the room.The energy from the sun has a short wavelength so it can to enter a room through the window but the energy is radiated by the objects,it has a longer wavelength so cannot escape
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What can this passive solar heating be compared to?
The Greenhouse Effect.
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How do wind turbines work?
They convert kinetic energy of moving air into electricity. The wind turns the turbines which turns the generator.
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How does the Sun cause wing?
ThEe energy from the sun heats the atmosphere which produces convection currents which causes wind.
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What are advantages of Wind power?
1. T`he turbines a cheap/easy to run 2.They're robust 3. Renewable(won't run out) 4. Doesnt pollute the atmosphere.
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What are disadvantages of wind power?
1.The amount of energy produced depends on the wind speed.2.Some people think it produces visual and noise pollution.3.They are expensive to set up 4. It can be difficult to find a suitable place.
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What is the National Grid?
Its a network of cables and pylons that transfers energy all over the country. It allows energy to be generated anywhere and supplied anywhere.
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How does a power station work?
1.The boiler heats water.2.water produces steam.3.The steam turns a turbine.4.The turbine turns the generator.5.The generator makes electricity.6. the steam condenses back into water and is recycled.
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What is the Dynamo effect?
Using electromagnetic induction to transform kinetic energy into electrical energy.
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What is electromagnetic induction?
The creation of a voltage in a wire which is experiencing a change in magnetic field.
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What two methods are there for the dynamo effect?
1. When an electrical conductor(coil of wire) is moved through a magnetic field.2. The magnetic field through an electrical conductor changes.
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How could you increase the voltage or current that you produced?
1. More coils of wire 2. A stronger magnet 3. A faster movement of the magnet or wire.
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Hw do generators use the dynamo effect?
1.The generators rotate a coil in a magnetic field.2Every half a turn, the coil changes direction.3.This produces an AC current (converse wave and the faster the coil turns, the more peaks and troughs on the wave)
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What is a step up transformer?
It is an appliance used to increase the voltage of the electrical power around the country.This means that the current of the power is low so less energy is wasted as heat(because higher currents means that the wires get hot so energy wasted as heat.
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What are step down transformers?
They are used to bring the voltage down to safe levels.
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Why is mains electricity and AC current?
The transformers only work on AC currents.
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What is the equation for energy efficiency?
ENERGY EFFICIENCY = USEFUL ENERGY OUTPUT divided by TOTAL ENERGY INPUTx 100
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What is the equation for Total energy input?
TOTAL ENERGY INPUT= USEFUL ENERGY OUTPU = WASTE ENERGY OUTPUT
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What is the equation for the power of an appliance?
Power(W)=Voltage(V)xCurrent(A)
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What is the equation for the energy supplied?
Energy Supplied(kWh)=Power(kW)xTime(hours)
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What is the equation for cost?
Cost=Number of unitsxPrice per unit.
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What is Off peak electricity?
Electricity supplied during the night
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What are advantages of off peak electricity?
1.Cheaper 2. Cost effective for electricity companies as power stations cant be turned off at night.
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What are disadvantages of Off peak electricity?
1.Risk of fire, no one is watching electrical appliances at night. 2. You have to fit part of your routine around the electricity at night just because its cheap.
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What is the greenhouse effect?
Some electromagnetic radiation with short wavelengths enters through the atmosphere and is absorbed by the earth. The earth warms up and radiates some of the infrared radiation with longer wavelengths so it is stuck in the atmosphere.
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How is more Carbon Dioxide being released?
We need more energy for the population so we grow more fossil fuels. More space is needed so forests are cut down . respiration
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How is more methane being released?
More cattle are used for our food and they produce methane in digestion. Decaying waste in landfill sites produces methane. Released naturally by wetlands, volcanoes and wild animals.
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How is more water vapour being released?
Power stations produce water vapour and it is produced naturally by seas,oceans,rivers.etc.
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What gas is causing an increase in the Greenhouse effect?
A rise in CO2 is causing global warming by increasing the Greenhouse effect.
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Changes in the earths temperatures can cause changes in weather patterns, how can this affect food production?
If areas become too dry or too wet to grow food then we wont have as much food production and this will get worse if the temperatures continued to increase.
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What are the natural and human causes to the earths temperature change?
Natural-1.volcanoes ash and gases can reflect suns radiation back to space which can cool the earth.2.Changes in our orbit can cause an ice age.Human-1.More CO2.2.Factory gases reflect heat from cities to the earth which can increase the temperature.
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WHat happens when an unstable nucleus decays?
It gives off nuclear radiation.e.g Alpha, Beta and Gamma
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What happens when the nuclear radiation causes ionisation?
It makes atoms lose or gain electrons which makes them ions.
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How can nuclear radiation cause cancer?
If the radiation enters human cells, it can ionise the molecules and damage DNA. This can lead to mutations in the cell that can cause cancer. High doses of radiation could kill the cell completely.
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What are features of alpha Particles?
They are big and slow with 2 protons and 2 neutrons. They are stopped by paper or skin so they are strongly ionising.(The less the radiation can penetrate before hitting an atom, the more ionising it is.)
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What are features of Beta particles?
They are small and fast. They are moderately ionising and can be stopped by a few mm of aluminium.
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What are features of gamma rays?
They have no mass and no charge. This radiation is weakly ionising as it can only be stopped by a few cm of lead.
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What is alpha radiation used for?
Smoke detectors have a small amount of alpha radiation that ionises the air and causes a current to flow between to electrodes. If theres a fire the current will stop and an alarm will sour.
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What is Beta radiation used for?
1.Beta/gamma is injected/swallowed by a patient and a detector on the outside of the body shows if the body is working properly.2.It detects thickness of objects.e.g paper by measuring how much radiation passes through.
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What is gamma radiation used for?
1.Used to kill cancerous cells .2.They sterilise medical instruments by killing the microbes(better than boiling as that can damage the instruments.3. They can see if things(e.g plane blades)are damaged if gamma is detected on other side.
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In a Nuclear power station, what is used to heat the water?
Nuclear fuel atoms(e.g.uranium)are split in two which releases heat and energy.
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What are the advantages of nuclear power?
1.Doesnt produce CO2 2.Releases a lot more energy, so a lot less of a nuclear fuel is needed.3.The nuclear fuel is relatively cheap.4.There is plenty of uranium in the ground
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What are th disadvantages of Nuclear power?
1.Expensive to build and maintain.2.Takes longer to start up the stations than fossil fuel ones.3.You have to process the uranium before use.4.It is very difficult to dispose of4.Non renewable.
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How can nuclear fuel be used for weapons?
The used uranium has to be reprocessed which can produce plutonium which can be used to make nuclear bombs.
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What do nuclear workers do to protect themselves from the radiation?
They wear full protective suits that stop radiation from being inhaled, lodging under skin or fingernails.etc
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How is Radioactive waste disposed of?
They have to be buried in boxes deep underground because they stay radioactive for thousands of years.
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What is the order of the planets?
Mercury, Venus, Earth, Mars(asteroid belt) Jupiter, Saturn, Uranus, Neptune
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What is a centripetal force?
The force that pulls an object to the centre of a circle to give it a circular motion.
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What caused the asteroid belt?
They were rocks that didnt form a planet because the gravitational force of Jupiter kept interfering.
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What are meteorites?
Rocks or dust that enter the earths atmosphere(shooting Stars)and burn up. We know they have already hit the earth as there are craters, unusual elements in rocks and sudden changes in fossil numbers between layers of rock.
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What are comets?
Balls of rock, dust and ices that orbit the sun in and elliptical orbit.As the comet gets close to the sun, the ice melts and creates a tail and they speed p as the gravitational pull is stronger.
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What are NEO's?
Near Earth Objects that could be on collision courses with the earth. For example, Comets/asteroids. Small ones could burn up in the earths atmosphere but large ones could cause explosions.Exploding bombs near one could nudge it into different course
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What is a theory about the formation of the moon?
A mars sized planet collided with the earth and the debris formed the moon.Evidence:Moon has a lower density than earth and no iron core unlike earth 2.moon contains rock that evaporates at low temp. suggesting moon was formed by hot material.
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Other cards in this set
Card 2
Front
What does direct current mean?
Back
The current flows the same way around the circuit all the time unlike AC current which changes direction all the time(like the mains in your home)
Card 3
Front
How do the photocells generate the electricity?
Back
Card 4
Front
What factors affect the amount of current produced?
Back
Card 5
Front
Give an advantage and disadvantage of a photocell
Back
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