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What are the advantages of photocells?
Robust, do not need much maintenance, they don't need fuel or long cables, cause no pollution and don't contribute to global warming, the use a renewable energy source
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What is the only disadvantage of photocells?
They do not produce electricity when it is too cloudy or dark
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What does a photocell contain?
Two pieces of silicon joined together to make a p-n junction
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What does the n piece of silicon involve?
It has an impurity added to produce an excess of free electrons
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What does the p piece of silicon involve?
It has a different impurity added to produce an absence of free electrons
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What are the energy packets in sunlight called?
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What do photons cause in a photocell?
They cause free electrons to move producing an electric current
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What does the output of a photocell depend on?
Light intensity, surface area exposed,distance from the light source
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What is the suns in fared radiations wavelength?
Very short
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Describe passive solar heating?
Glass is transparent to the short wavelength radiation(from sun), the walls and floors inside the building absorb the radiation, the walls and floor warm and re-radiate the radiation, the glass reflects the radiation back into the building
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Why does the glass reflect the re-radiated radiation?
Because the walls and floor are not as hot as the sun and the wavelength radiated is therefore longer, the glass reflects the re-radiated radiation because its got a longer wavelength
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Why are solar reflectors moved by computers?
To make sure they are always facing the sun
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When do wind turbines not work?
When there is no wind or the wind speed is too great
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What are the disadvantages of wind turbines?
Noisy, take up a lot of space and people sometimes complain the spoil the view
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How can the current from a dynamo be increased?
Using a stronger magnet, increasing the number of turns on the coils, rotating the magnet faster
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What does a oscilloscope do?
Displays the output from a dynamo
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What does an oscilloscope trace show?
How the current produced with a dynamo varies with time
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In an oscilloscope what is the time for one complete cycle called?
The period of the alternating current
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What does a simple generator consist of?
A coil of wire rotating between the poles of a magnet?
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In a generator how is the magnetic field involved?
The coil cuts through the magnetic field as it spins
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Where is the current produced in a generator?
In the coil
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What are the three steps for producing electricity?
Water boils to produce steam, steam at high pressure turn the turbine, the turbine drives a generator
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What does efficiency measure?
How well a device transfers energy
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Where is energy lost in a power stations?
In the boilers, generator,cooling towers
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How does carbon dioxide naturally occur in the atmosphere?
Volcanic eruptions, decay of dead plants, natural forest fires, respiration, escape form the oceans
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Where does man-made carbon dioxide come from?
Burning fossil fuels, water incineration, deforestation, cement manufacture
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What is the most significant greenhouse gas?
Water vapour
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What are the man made sources of methane?
Mining and burning of fossil fuels, digestion process in animals like cattle, landfill
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What are the natural sources of methane?
Wetland, termites, oceans
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Describe the green house effect in terms of wavelengths?
Radiation from the sun has a short wavelength, the radiation is absorbed and warms the earth, the earth them re-radiates the radiation as a longer wavelength, the longer wavelength is absorbed by the green house gases which warms atmosphere
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How does the smoke from factories effect the atmosphere?
The smoke reflects the radiation from the factory back to earth, the temperature rises
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How does an ash cloud from a volcano effect the atmosphere?
The ash cloud reflects radiation from the sun back into space, the temperature drops as a result
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What units do electrical appliances display power ratings in?
Watts(W) or kilowatts(kW)
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What's the unit for electrical energy used in the home?
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When do we pay less for electricity and why?
At night, not as much is needed but it still has to be produced
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What factors effect the choice of energy sources?
Availabilty, ease of extraction, effects on the environment, associated risks
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What is the national grid?
A series of transformers and power lines that transport electricity from the power station to the consumer
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Why are step up transformers used in the national grid?
Reduce energy loss, reduce distribution costs, cheaper electricity for consumers
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Why are transformers nearer the consumer used to step down the voltage?
To make the voltage a more suitable level for the consumer
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The greater the current, the .......... the ..... Fill in the gaps
Hotter the wire
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When a transformer increases the voltage the current is reduced, why?
it means there is less heating effect and therefore less energy lost to the environment
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What happens when an atom gains an electron? What happens when an atom loses an electron?
Gains-becomes negatively charged Loses- becomes positively charged
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What is the process called when atoms gain or lose electrons?
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Where does gamma, beta,alpha radiations come from?
The nucleus of an atom
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Out of gamma, beta and alpha radiation what cause the most and least ionisation?
Most:alpha Least:gamma
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Describe alpha radiation?
Short ranged(few cm) and easily absorbed a by a sheet of paper, card, skin
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Describe beta radiation?
Range of about 1m and is absorbed by a few mm of aluminium
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Describe gamma radiation?
Very penetrating, a few cm of lead will stop the radiation,some gamma radiation can pas through several metres of lead or concrete
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What has to be taken into account when experiments are done with radiation
Background radiation
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How do smoke alarms use alpha radiation?
The radiation ionises the nitrogen and oxygen atoms in the air which creates a small electric current that is detected, when smoke fills the detector in the alarm during a fire,air isn't ionised, so current is less,alarm sounds
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How does beta radiation and a detector control the thickness in a paper rolling mill?
The amount of radiation passing through the sheet is monitored and adjusted accordingly
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What is gamma radiation used for?
It kills microbes and bacteria so is used to sterilise medical equipment, and can be used to check for leaks in pipes and welds
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What is a waste product from nuclear rectors and what can it be used for?
Plutonium and to make nuclear bombs
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Where is low level radioactive waste can be disposed of?
Buried in land fill
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Where is high level radioactive waste can be disposed of?
Encased in glass and buried deep underground or reprocessed
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Why should nuclear waste not be stored near water supplies?
So cannot leak into them and terrorists cant use it to contaminate water supplies
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What are the advantages and disadvantages of nuclear power?
Advantages: fossil fuels reserves are not used and no green house gases are discharged into the atmosphere Disadvantages: Very high maintenance and decommissioning costs and there is a risk of accidents
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What are the orders of planets from the sun?
Mercury, venus, earth, mars, jupiter, saturn, uranus, neptune,pluto
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What type of orbits do comets have?
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Describe a meteor?
Made from grains of dust that burn up as they pass through the earth atmosphere, they heat the air around them which glows and the streak is known as a shooting star
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What are the features of a black hole?
Formed where large stars used to be, you cant see black holes because no light can escape from it, it has a large mass but a very small size
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Why do moons orbit planets?
Because a centripetal force acts on them
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What are some features of a spacesuit?
A dark visor to stop the astronaut being blinded, the suit is pressurised and has an oxygen supply for breathing,
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What are advantages and disadvantages of an unmanned spacecraft?
No way of repairing them if they break down, they cost less, do not put astronauts lives at risk, can go in conditions deadly for humans
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What are advantages and disadvantages of a manned spacecraft?
Have to carry large amounts of food,fuel and water,expensive, astronauts can die, cant go into certain conditions
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How fast is light?
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What's a light year?
The distance light travels in one year
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What are asteroids?
Mini planets or planetoids orbiting the sun, most orbit between Mars and Jupiter, they are large rocks left over from the formation of the solar system
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How were all bodies including planets in space formed?
When clouds of dust and collapse together due to gravitational forces of attraction
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Fill in the gaps.........the bigger the......the....... the gravitational force
The bigger the mass the greater the gravitational force
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How do scientists believe our moon was formed?
It was the result of a collision between two planets in the same orbit, the iron core of the other planet melted and joined with the earth core, less dense rock began to orbit and join together to become the moon
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What scientific evidence is there to support the theory of the moon?
The earth is more dense than the moon, there is no iron in the moon, the earth and moon have exactly the same oxygen composition other planets have different compositions.
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What evidence is there that asteroids have collided with earth?
Near a crater that was thought to be from an asteroid, they found quantities of the metal iridium which is not normally found on the earth' crust, fossils around found below the layer of iridium but not above it, tsunamis have disturbed fossil layers
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Where do comets pass?
Pass inside the orbit of mercury and well beyond the orbit of Pluto
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What's a comet made from?
Dust and ice
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What happens when a comet passes close to the sun?
The ice melts and the solar winds blow the dust into the comets tail which always points away from the sun
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What happens to a comet speed nearer the sun and why?
The speed increases as it approaches the sun and decreases as it gets further away,, this is because of the changing gravitational attraction
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What does NEO stand for?
Near earth object
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What precautions would be put in place to avoid a collision with an NEO?
One option, explode a rocket near the NEO to alter the course enough to miss earth
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What are most of the galaxies doing? And what are the furthest galaxies doing?
They are moving away from each other, the furthest galaxies are moving away the fastest
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What did Galileo confirm with the telescope?
He observed the four moons of Jupiter and confirmed not everything orbited the earth
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What was Copernicus' theory?
That planets orbit the sun
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Why did the Catholic Church disagree with Galileo's theory?
Because they believed the earth was at the centre of the universe
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What was Newtons theory?
Universal gravitation which suggests all bodies attract each other.
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Today, why do we believe that gravitational collapse is prevented?
Because the universe is constantly expanding due to the big bang
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What is red shift?
When a source of light is moving away from an observer, its wavelength appears to increase which shifts light towards the red end of the spectrum
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How can scientists use red shift?
To find out the age of the universe
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What is a nebula?
A swirling cloud of dust and gas
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How is a protostar formed?
Nebula clouds are pulled together by gravity, as the swirling ball of gas starts to get it hot is glows, this is a protostar
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Why can't the protostar be seen?
Because of the dust cloud
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Describe nuclear fusion in a protostar?
Gravity causes the start to become hotter,smaller and brighter,after millions of year the core is hot enough for nuclearfusion,as hydroge nuclei join together to form a helium nuclei, energy is released and star shines while there is enough hydrogen
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Why do small stars shine for longer than large stars?
Because they have less hydrogen but use it up at a slower rate
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At the end of medium sized stars life what happens?
It becomes a red giant, the core contracts and the outer part cools+changes colour from yellow to red, +expands,planetary nebula(gas shells) are thrown out,the core=white dwarf, then cools and becomes as black dwarf
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What happens when a large star dies?
Become red super giants,as core contracts outer part expands,core collapses to form a neutron star, then there is an explosion called a supernova
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What can remnants of a super nova form?
A new star
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What happens if the core of the dense neutron star continues to collapse?
Becomes even more dense and could form a black hole,
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Black holes have a very large mass concentrated in a small volume, what does this mean in terms of density and gravitational pull?
It means it has a very large density, and the large mass means it had a strong gravitational pull
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Other cards in this set

Card 2


What is the only disadvantage of photocells?


They do not produce electricity when it is too cloudy or dark

Card 3


What does a photocell contain?


Preview of the front of card 3

Card 4


What does the n piece of silicon involve?


Preview of the front of card 4

Card 5


What does the p piece of silicon involve?


Preview of the front of card 5
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