P2

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  • Created by: dkoning00
  • Created on: 08-06-16 18:31
How is some of the Sun's energy stored naturally on Earth?
In fossil fuels
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How is harnessing wind energy indirect use of the Sun's energy?
Sun heats the air; hot air rises; air moves turbines
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What are photocells?
Devices that generate electricity directly from the Sun's energy
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What type of current is created by photocells?
DC (Direct Current)
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What are photocells usually made of and why?
Silicon because it is a semi-conductor
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Describe how photocells generate electricity
Silicon atom absorbs some of the energy form the Sun; some electrons are knocked of the atom's outer shell; the dislodged atoms flow around the circuit creating an electrical current
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What three factors affect the power output of a photocell and how?
The surface area - the bigger the SA the more electricity produced. The light intensity - brighter light = more electricity. The distance from light source - the closer the source, the more intense the light is
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Give three advantages and explanations of photocells
No moving parts so low maintenance and last longer. No need for power cables or fuels so good for low power devices e.g. calculators. Solar power cannot run out (it's renewable) and doesn't pollute the environment at all so is sustainable.
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What is the biggest disadvantage o solar power?
When there's no sunlight (e.g. at night), there's no power so it is difficult to be totally reliant on it
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Other than photocells, how can the Sun's energy be harnessed?
Curved mirrors can be focused to concentrate energy
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In what ways can curved mirrors be used?
Food can be heated on the focal point in poor countries or ones without electricity. Large curved mirrors can be used to heat water pipes in order to generate steam that spins turbines and creates electricity
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How can solar devices like solar panels and curved mirrors have increased efficiency?
If they track the Sun's movement across the sky and are pointed directly at the Sun then they capture the maximum amount of light and heat
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What is passive solar heating?
The sun's energy being used to heat something directly i.e. without mirrors, lenses or photocells
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Why is glass important in passive solar heating for a house?
Glass lets heat and light from the Sun into the house; it is absorbed by objects thus heating them up. Objects then remit the infrared energy but with a longer wavelength so they cannot escape, waves stay in the house to heat it - greenhouse effect
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How can passive solar heating be used to heat water?
Matt black pipes in a glass box on the roof of a house are heated by the greenhouse effect which heats water being pumped through them - the water can then be used in radiators, washing machines etc.
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How do wind farms produce electricity?
Sun heats air, air moves, kinetic energy turns turbine blades, spins generator and generates electrical current
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What are the advantages of wind turbines?
They are cheap to run as they are reliable and wind is free. No polluting waste or products.Renewable energy source.
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What are the disadvantages of wind farms?
1 coal power station=1500 wind turbines; visual & noise pollution - can spoil views and are noisy; wind isn't always fast enough to produce electricity; supply cannot be increased with demand; suitable sites are hard to find; expensive to build
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What is the National Grid?
A network of pylons and power lines that transport electrical power across the country from power stations to homes and industry
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Describe how power stations relase energy
Fuel is burned to turn water into steam in a boiler; steam moves through a turbine to trun the blades; the rotation is converted into electrical energy in a generator then transferred by cables
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What are the advantages and disadvantages of fossil fuels being burned in power stations
They are readily available and are a concentrated source of energy. However, they release CO2 and cause acid rain plus we have no control over supply or price because they are bought from other countries
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Advantages and disadvantages of Biomass fuels?
It is carbon neutral and can be quickly obtained, but it doesn't have as high of an energy value as fossil fuels
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What is electromagnetic induction?
The creation of volatage (and possibly current) in a wire that is experiencing a change in the magnetic field
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What is the dynamo effect and how is it used?
Using electromagnetic induction to turn kinetic energy into electrical energy - used in power stations by turbines creating electricity
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What type of current is produced and why?
AC -because the movement causes alternating voltage
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How can you get a bigger current and voltage?
Increase the strength of the magnet, the number of turns on the coil and the speed of the movement
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How do generators work?
By turning a coil in a magnet to produce an AC current
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In terms of voltage display, describe what happens to the waves when increasing the speed of rotation and why
They increase in both frequency and amplitude because the coil is passing the magnet more times per second and faster so there is a higher voltage
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What is frequency measured in?
Hertz
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Describe the difference between AC and DC current and give an example for each of a device that produces it
AC is constantly cycling from positive to negative voltages - created by generators. DC remains at one constant positive voltage - created by a battery or photocell
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Give the equation for power loss
Power loss = Voltage x Current squared
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Why is electricity transported at a high voltage across power lines from power stations?
Because power loss = voltage x current squared so a higher voltage means lower current and much less power loss - it is more efficient
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How is voltage increased when leaving a power station?
By a Step-up transformer
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Why must the voltage be decreased again before use and how is this done?
So it is safe and doesn't damage devices - step-down transformer
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Why do transformers only work on AC current?
Because they use electromagnetic induction
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Why do most power stations have low efficiency?
Because a lot of energy is wasted as heat and noise to the surroundings
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What is power measured in?
Watts
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Give the equation for power
Power (W) = Voltage (V) x Current (A)
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What is a Kilowatt hour?
A unit of electrical energy used - the amount of electrical energy converted by a 1kW appliance left on for one hour
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Give the equation for energy supplied in kW/H
Energy supplied = Power (kW) x Time (Hrs)
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Cost of electricity =
Number of units used x Price per unit
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What is 'off-peak' electricity and why do some people use it?
Using electrical appliances at night and in the early morning when few other people are using it. Electricity is cheaper off-peak so can reduce energy bills
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What are some of the disadvantages?
Some argue that appliances could cause fires in a house if unattended over-night. Also it is inconvenient to only use certain appliances at night
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Briefly describe the greenhouse effect
Short wavelength EM waves pass through the atmosphere from the sun; they heat the surface of the Earth which then re-emits longer wavelength EM waves; These are blocked from leaving atmosphere by greenhouse gases; the gases trap heat to raise temp.
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Give the three main greenhouse gases
Carbon dioxide, Methane and Water vapour
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Why are greenhouse gases both vital to our existence and a threat to it?
Without them the Earth would be too cold for life, however, too much will raise the average temp. which would also make the Earth uninhabitable
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Why have Carbon dioxide levels risen in the last 200 years?
People use more energy (e.g. travel more in cars) which means more fossil fuels are burned; more trees are being cut down to make space so less photosynthesis; more people also means more respiration
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Why have methane levels risen?
Cattle farming has increased which releases methane; increasing decaying waste in landfill; also released by volcanoes, wetland and animals
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Why have water vapour levels rise?
Increased global temp. means more evaporation from water sources; power stations also produce water vapour
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What are the three kinds of nuclear radiation?
Alpha, beta and gamma
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What is ionisation?
Atoms losing or gaining electrons
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How can radiation be dangerous to humans?
Molecules in cells ionise which damages DNA causing mutations and possibly cancer. Very high doses can also kill cells completely
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What is the ionising power of each kind of radiation linked to and how?
How far it can penetrate - the more penetration before hitting the atom the less ionising it is
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Describe the features and properties of Alpha decay
Big, heavy, positive isotopes consisting of 2 protons and 2 neutrons that moves slowly and as a result cannot penetrate far. Can be blocked by thin paper or skin but are heavily ionising.
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Describe the features and properties of Beta decay
Small, fast moving, negative electron that penetrate further than alpha so less ionising. Can be stopped by a few mm of aluminium
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Describe the features and properties of Gamma decay
Left over energy released from the nucleus as EM wave - no mass, no charge and can penetrate a long way so not very ionising at all. Can be stopped by thick concrete and a few cm of lead
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Which type is most dangerous if ingested and why?
Alpha because it is the most heavily ionising so ca cause mutation and death of cells
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How could you tell which kind of radiation is being emitted?
By measuring what materials and what thicknesses it can penetrate which a Geiger counter - e.g. if still measuring radioactivity beyond an aluminium plate then it must be gamma
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How is Alpha radiation used in smoke detectors?
Small source of alpha radiation put close to 2 electrodes. Air between them is ionised allowing current to flow between electrodes completing a circuit. If smoke in air it absorbs the radiation so air isn't ionised, the circuit breaks & alarm sounds
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Give three other uses of radiation and the types used
Medical and industrial tracers (gamma & beta), testing paper thickness (beta), treating cancer (gamma), sterilising medical equipment (gamma)
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What is nuclear fission?
Splitting heavy nuclei to release energy
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How is it used in a nuclear power station?
Unstable uranium atoms are split into two which releases energy as heat to heat water into steam which spins turbines attached to a generator
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Give advantages of nuclear power
Lots of energy without CO2; much higher energy value with radioactive fuels - less fuel needed to make same amount of energy as fossil fuels; uranium is relatively cheap; High amounts of Uranium left to be extracted
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Give disadvantages of nuclear power
Power stations are expensive to build & maintain; long start-up time; processing uranium causes pollution; always a risk of leaks and disaster; radioactive waste; decommissioning is expensive and difficult; uranium isn't renewable
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What happens to used uranium fuel?
It can be reprocessed to get a smaller amount of uranium that can be re-used and a bit of plutonium that is used in nuclear weapons
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What measures should be taken when handling radioactive material?
Avoid ingestion and inhalation; store safely in lead container; minimise exposure time; do not point it at yourself or others; do not touch with bare skin; keep at arm's length
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What measures must industrial nuclear workers take?
Wearing full protective clothing with breathing apparatus; lead lined suits, walls and screens; using robotic equipment to remove human contact
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How can radioactive waste be disposed of?
Low-level waste is buried in landfill, high level radioactive waste is treated, sealed in glass blocks, placed in metal canisters and buried deep underground
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What are some of the difficulties with finding suitable locations to dispose of high-level radioactive waste?
The ground must be geologically stable (not prone to earthquakes etc.) and cannot be near a major water source
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Why is most high-level waste kept on site at power plants?
Because finding a location is difficult and many people object to disposal so keeping it on site is easier
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Why do nuclear power stations need to be kept secure?
Because they could be targets fro terrorist attacks and the material inside could be used to make 'dirty bombs'
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List the contents of our solar system
The Sun, Mercury, Venus, Earth, Mars, (Asteroid Belt), Jupiter, Saturn, Uranus, Neptune, (Pluto)
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What keeps planets in orbit around a star?
A combination of the planet's forwards motion perpendicular to the star and the gravity pulling the planet directly towards the star resulting in circular motion
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What is this force known as?
Centripetal force
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What is the asteroid belt and why did it form?
Millions or rocks in a ring around the Sun between Mars and Jupiter - these rocks should have come together to form a planet in the early stages of the solar system but Jupiter's gravity kept interfering so they didn't come together
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What are meteors?
Rocks or dust that enter the Earth's atmosphere then burn up appearing as 'shooting stars'
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What are meteorites?
Pieces of a meteor that did not completely burn up when entering the atmosphere impacting the surface of the Earth.
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How can meteorites be dangerous?
On impact they can create craters, start fires and throw large amounts of dust and smoke into the atmosphere causing climate change
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Give an example of a historical meteorite impact and its effects
Around 65 million years ago an asteroid roughly 10km in diameter impacted the Yucatan peninsular in Mexico which kicked dust and smoke up into the atmosphere causing global temperatures to drop drastically. This resulted in extinction of many species
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What evidence can be used to show where asteroids have previously landed?
Craters in the ground; layers of unusual rock/elements that were 'imported' by an asteroid; sudden changes in fossil numbers as species were extinct
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What are comets?
Balls of dust, ice and rock which orbit stars in very elongated ellipses often in different planes from the planets
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Briefly describe the stages of a comet's orbit starting from the Sun
Comet travels very quickly around the Sun close to it; sling-shot away at high speed; The further away it gets, the slower it becomes dues to gravity; it turns back towards the Sun due to its attraction accelerating; highest speed when it reaches Sun
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Why does a comet's acceleration increase as it gets closer to the Sun?
Because the gravitational attraction is stronger as it gets closer
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What are Near Earth Objects?
Asteroids or comets which could be on a collision course with Earth or pass close by it
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How can they be dangerous?
If a large NEO impacted Earth it could cause explosions, tsunamis, earthquakes, a nuclear winter and the end of every human ever... like seriously
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How are NEOs monitored and how could an impact be averted?
Monitored using telescopes and satellites - if a powerful enough explosion occur close enough to a large asteroid it could knock it off course e.g. launching a nuclear missile... Failing that, Bruce Willis
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Describe briefly how scientists believe our moon was formed
A Mars-sized planet (Thea) collided with the Earth; the iron cores merged under intense heat and pressure to form modern Earth; less dense surface material ejected into space; rocks orbited Earth and forged together to make the moon in orbit
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What evidence is there to support this theory?
The Moon has a lower density than Earth and has no iron core suggesting it is made of crust rock and Moon rock contains few materials that evaporate easily meaning it was formed under intense heat
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What galaxy is our solar system in?
The Milky Way
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What is a light year?
The distance light travels through a vacuum in one year
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Why do scientists use light years instead of kilometers when measuring space?
Because things are so far apart that they would have to use ridiculously large measures of kilometers. Light years are so much larger that they a more appropriate unit of measurement
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Roughly how far is one light year?
Over 9 quadrillion
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What is a black hole?
When very massive stars run out of fuel they can explode leaving an incredibly dense core - nothing can escape its gravitational attraction (not even light)
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What difficulties are associated with manned space travel?
The craft must carry lots of food, water and oxygen; temperature and gas content must also be regulated; craft must have radioactive shielding; long periods of zero gravity diminish muscle ad bone strength; psychological stress
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What are the three types of probe mission and what are they used for?
Fly-by - gathers data on temp. magnetic & gravity attraction and radiation without entering atmosphere. Entering atmosphere - collects similar data as well as atmospherical content. Landing - rovers land on surface to collect physical samples
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Give advantages of unmanned spacecraft
Don't have to carry food, water or oxygen; can withstand conditions lethal to humans; no people taking up space and weight; cheaper, less safety equipment etc.; no potential for loss of life
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Give disadvantages of unmanned spacecraft
Probes cannot think for themselves whereas humans can solve problems to survive; cannot do maintenance/repairs like astronauts e.g. Apollo 13, Discovery etc.
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What two ways can data be sent back to Earth and when are they appropriate?
'Beaming' - sending digital data over long distances by radio waves from far away probes usually; Physical data can be sent back if the craft returns - astronauts collect moon rock etc.
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Why is it believed that the universe is expanding?
Galaxies all appear to be moving away from each other
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What is red shift?
Light from distant galaxies have lower frequencies than expected (shifted towards red end of spectrum). This means that the sources of the light (galaxies) are moving away from us very quickly
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Why do more distant galaxies have greater red shift?
Because they are moving away faster than nearer galaxies concluding that the universe is expanding in all directions
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What is Cosmic Microwave Background Radiation (CMBR)?
Scientists detect low frequency microwave radiation in space from all directions. It is strong evidence supporting the Big Bang Theory
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Briefly describe the Big Bang Theory
Roughly 14 billion years ago all matter in the universe occupied an exceptionally small space (smaller than a pinhead); it then 'exploded' thus expanding the space and matter in all directions continuously
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What is a nebular?
A huge cloud of dust and gas in space
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How are Protostars formed?
Nebulars gain gravitational attraction and spiral together creating high pressure and heat
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When is a main sequence star formed?
When the temperature gets high enough for hydrogen to undergo thermonuclear fusion to form helium nucle and release huge amounts of heat and light energy. The fusion provides outward pressure to counter gravity keeping the star stable
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What happens when the hydrogen runs out?
Fusion stops so the star swells and the surface cools - a red giant is formed
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Describe the rest of the life-cycle for a small to medium sized star
The red giant ejects it outer layers of dust and gas to become a planetary nebular; hot, dense core is left behind (white dwarf) until it cools and fades into a black dwarf and disappears
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Describe the rest of the life-cycle for a more massive star
Forms super red giant which glows brightly and contracts and expands several times as heavier elements are made by fusion; explodes into a supernova; very dense core is left behind as a neutron star; if big enough, it will collapse into a black hole
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What does geocentric mean and what was the Ptolemaic model?
Earth centred - Model of the solar system used by the Greeks with the Sun, Moon, planets and stars all orbiting the Earth in the centre
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What does Heliocentric mean and what is the Coppernican model?
Sun centred - Model of the solar system introduced by Coppernicus in 1543 with the sun in the middle being orbited by the planets in perfect circles
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How did Galileo find good evidence to support Coppernicus?
By studying Jupiter with a telescope he noticed some stars didn't ever move away from Jupiter. He figured out these stars were actually moons orbiting Jupiter which proved that not everything orbited Earth. He also noticed phases of Venus
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Why wasn't the Coppernican model initially accepted?
Because it contradicted an accepted theory that had been around for centuries, also it was condemed by the church
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How did it come to be accepted?
With the development of new technologies more evidence could be gathered
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How is the modern model slightly different to the Coppernican Model?
It still has the planets all orbiting the sun but it slightly elliptical orbits, also, the Coppernican model claimed the stars were fixed around the solar system but we now know this to not be true
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Card 2

Front

How is harnessing wind energy indirect use of the Sun's energy?

Back

Sun heats the air; hot air rises; air moves turbines

Card 3

Front

What are photocells?

Back

Preview of the front of card 3

Card 4

Front

What type of current is created by photocells?

Back

Preview of the front of card 4

Card 5

Front

What are photocells usually made of and why?

Back

Preview of the front of card 5
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Comments

Bushra Patel

This is pretty good set, thanks loads, I've been trying to find a good P2 set and this is excellent 'cause it's shorthand and easy to remember, so thanks loads 

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