P2- Living for the Future (Energy Resources) Flashcards
What are the advantages of photocells?
- robust and do not need much maintenance
- no fuel and long power cables needed
- cause no pollution and do not contribute to global warming
- use a renewable energy resource
What is the only disadvantage of photocells?
Do not produce electricity when it is dark or cloudy
What does a photocell contain?
Two pieces of silicon joined together to make a p-n junction
What does the n-type and p-type silicon contain?
N-type silicon
Has an impurity added to produce an excess of free electrons
P-type silicon
Has a different impurity added to produce and absence of free electrons
What does sunlight contain?
Energy packers called photons
What does the photon do?
Cause free electrons to move producing an electric current
What does the output of a photocell depend on?
- light intensity
- surface area exposed
- distance from light source
How does passive solar heating work?
- sun produces infrared radiation with short wavelengths
- glass is transparent to this short wavelength radiation
- walls and loor inside a building absorb radiaion, warm up and re-radiate infrared radiation
- walls and floor are not as hot as the Sun and the wavelength radiated is therefore longer
- glass reflects this longer wavelength radiation back inside the building
What is a disadvantage of wind turbines?
- do not work if there is no wind
- or if the wind speed is not too great
What are advantages and disadvantages of wind farms?
Advantages
- do not contribute to global warming
- do not pollute the atmosphere
Disadvantages
- noisy
- take up a lot of space
- visual pollution
How can you increase the current from a dynamo?
- stronger magnet
- increasing the numebr of turns on the coil
- rotating the magnet faster
What does an oscilloscope show?
The output from a dynamo- how the current produced by the dynamo varies with time
What is the period of the alternating current?
The time for one complete cycle
What does a generator consist of?
A coil of wire rotating between the poles of a magnet:
- coil cuts through the magnetic field as it spins
- current is produced in coil
What is an alternative generator method?
If the coil remains stationary and the magnets move
How do generators at power stations work?
Coil remains stationary and magnets move
In conventional power stations, how are fuels used to heat water?
- water boils to produce steam
- steam at high pressure turns a turbine
- turbine drives a generator
How can you measure energy efficiency?
efficiency =
useful energy output / total energy input (x100%)
What type of EM wave is absorbed by the atmosphere?
Infrared radiation
What adds carbon dioxide into the atmosphere?
- natural forest fires
- volcanic eruptions
- decay of dead plant and animal matter
- its escape from the oceans
- respiration
What is man-made carbon dioxide caused by?
- burning fossil fuels
- waste incineration
- deforestation
- cement manufacture
How is water vapour made?
- almost all water vapours occurs naturally
- 0.001% comes from human activity
How is methane produced?
When organic matter decomposes in an environment lacking oxygen
Where is methane usually produced?
- natural sources e.g. wetalnds, termites and oceans
- man-made sources e.g. mining and burning fossil fuels, digestive processes in animals (cattle), rice paddies and burying waste in landfills
What wavelength is EM radiation from the Sun?
Relatively short wavelength
What does the Earth do to the Sun’s radiation?
Absorbs it and warms the Earth. The Earth then re-radiates the energy as infrared radiation with a longer wavelength. This is absorbed by the greenhouse gases which warms the atmosphere
What does dust in the atmosphere do?
- smoke from factories reflects radiation from the town back to Earth. The temperature rises as a result
- ash cloud from a volcano reflects radiation from the Sun back into space. The temperature falls as a result
How can you calculate power?
Power = voltage x current
How can you calculate energy supplied?
energy supplied = power x time
How can you calculate cost of electricity?
Cost of electricity used = energy used x cost per kWh
When are the off-peak hours using electricity?
At night, electricity is cheaper because it is not as needed
What does the choice of energy sources depend on?
- availability
- ease of extraction
- effect on environment
- associated risks
What is the National Grid?
A series of transformers and power lines that transpor electricity from the power station to the consumer
What does the high voltage of the National Grid lead to?
- reduced energy loss
- reduced distribution costs
- cheaper electricity for consumers
What is used to increase the voltage of the National Grid to 400,000V?
A step-up transformer
What is used to lower the voltage to make it safe for consumers?
A step-down transformer
What does a high current lead to?
A hotter wire, and therefore energy wasted
What happens to the current when the voltage is increased?
The current is reduced so less energy is lost to the environment, so it is more efficient
What are atoms?
Basic ‘building blocks’ of an element which cannot be chemically broken down
What charge are atoms?
Neutral (they contain the same number of protons and electrons)
What is ionisation?
Involves gaining or losing electrons
- atom gains electrons, becomes negatively charged
- atom loses electrons, becomes positively charged
How can ions cause chemical reactions?
May disrupt normal behaviour of molecules inside the body
Where do alpha, beta and gamma radiation come from?
The nucleus of an atom
What is the order of most ionising to least ionising?
Most- Alpha
Beta
Least- Gamma
What can penetrate alpha and what is its range?
It can be easily absorbed by a sheet of paper or card
Short ranged (a few centimetres)
What is beta’s range and what can penetrate it?
Range of about 1 m
Absorbed by a few millimetres of aluminium
What is gamma’s range and what can penetrate it?
Most penetrating and can be stopped by a few centimetres of lead, but can pass through several metres of lead of concrete
How is alpha radiation used in smoke alarms?
- radiation ionises oxygen and nitrogen atoms in air
- causes a small electric current that is detected
- smoke fills the detector in alarm during a fire
- air is not ionised
- current is less
- alarm sounds
How is beta used to detect paper thickness?
- amount of radiation passing through sheet is monitored
- pressure on rollers adjusted accordingly
What is gamma radiation used for?
- kills microbes and bacteria
- sterilising medical instruments
- check for leaks in piped and welds
What type of radition can be used to trace the passage of blood and other substances around the body?
Beta or gamma
Why is alpha not used to trace the passage of blood and other substances around the body?
It would not be able to escape the body, so would ionise the insides
When doing an experiment to identify the type of radiation from its penetrating power, what must be taken into account?
The backround radiation
What element is a waste product from nuclear reactors?
Plutonium
What can plutonium be used for?
Making nuclear bombs
Where can low level radioactive waste be put?
Buried in landfill sites
Where is high level radioactive waste put?
Encased in glass and buried deep underground or reprocessed
What must be taken into account when radioactive waste is stored?
That it cannot leak into natural underground water supplies and into lakes and rivers. It could be used by terrorists to contaminate water supplies or areas of land
What are advantages of nuclear power stations?
- Fossil fuel reserves are not used
- No greenhouse gases are discharged into the atmosphere
What are disadvantages of nuclear power stations?
- Very high maintenance
- Decommissioning costs
- Risk of accidents similar to the one at Chernobyl
What is a comet?
Lumps of rock and ice found in space - some orbit the Sun
What shape is a comet’s orbit?
Elliptical
Where does a comet enter and leave?
They pass inside the orbit of Mercury and go out well beyond the orbit of Pluto
What is a meteor?
Bright flashes in the sky caused by rocks burning in Earth’s atmosphere
What are meteor’s made up of?
Grains of dust
What is a ‘shooting star’?
The meteor heats the air around them, which glows and the streak is the shooting star
What is a black hole?
A region of space from which nothing, not even light, can escape
How are black holes formed?
Where large stars used to be (has a very large mass but small size)
What is centripetal force?
Force acting on a body, travelling in a circle, which acts toward the centre of the circle and keeps the body moving in a circle
Why do moons orbit planets and planets orbit stars?
- The centripetal force acts towards the centre of the circular orbit
- Gravitational attraction is the source of the centripetal force
What are the advantages and disadvantages of using unmanned probes to go to space?
Advantages
- can go where conditions are deadly for humans
- cost less (less room for humans, no need for food supplies)
- do not put lives at risk
Disadvantages
- cannot be replaced if broken
What are the advantages and disadvantages of using astronauts to go to space?
Advantages
- humans can repair damages that a robot cannot
Disadvantages
- the spacecraft would have to carry humans and food and supplies that would allow them to survive
- it puts lives at risk
- humans do not live very long
What do astronauts need to wear in space?
- dark visor to stop them being blinded
- suit that is pressurised and has oxygen for breathing
- surface of the suit facing towards the Sun can reach 120°C
- surface of suit facing away from the Sun can be as cold as -160°C
How far does light travel?
300,000 km/s
Light from the Sun takes about 8 minutes to reach Earth
What are asteroids?
Composed of rock or metallic material orbiting the Sun in a region between Mars and Jupiter
Where is the Asteroid Belt located?
Between Mars and Jupiter
How were all the bodies in space formed?
When clouds of gas and dust collapsed together due to gravitational forces of attraction
What does the mass of an object determine?
Its gravitational force
What does Jupiter’s gravitational force do to asteroids?
Prevent them from joining together to forma another planet
How did scientists believe the Moon was formed?
A collision between two planets in the same orbit. The iron core of the other planet melted and joined with the Earth’s core, less dense rocks began to orbit and they joined together to form the Moon
What scientific evidence explains the theory about the Moon’s formation?
- average density of Earth is 5500 kg/m3 while Moon’s is onl 3300 kg/m3
- the moon has no iron
- the Moon has exactly the same oxygen composition as the Earth, but rocks on Mars and meteorites from other parts of the Solar System have different oxygen compositions
What evidence have geologists found about asteroids colliding with Earth?
- metal iridium was found near crater sites (Earth’s crust does not contain iridium, but asteroids do)
- fossils are found below the layer of iridium but not above it
- tsunamis have disturbed fossil layers, carrying some fossil fragments up to 300km inland
What happens to the comet when it is near the Sun?
It’s orbit speed is faster and the ice melts, producing a ‘tail’ that always points away from the Sun
What is a NEO?
Near-Earth Objects
Why do scientists need to monitor NEO’s?
Because they need to ensure it does not crash into Earth
Why does a comet’s speed increase as it approaches the Sun?
The gravitational attraction is much stronger when it is near the Sun
What can be done to avoid an NEO colliding with Earth?
To explode a rocket near the NEO which could alter its course enough to miss Earth
What is the expanding Universe theory?
Almost all the galaxies are moving away from each other with the further galaxies moving fastest
What did Galileo do?
Used a telescope to observe the four moons orbiting Jupiter and confirmed Copernicus’ idea that planets orbited the Sun
Why did the Roman Catholic church not approve of Galileo’s model?
They believed that Earth was at the centre of the universe
What was Newton’s theory in the 17th century?
The theory of universal gravitation which suggested that all bodies attract one another
Why is it believed that gravitational collapse is prevented?
Because the universe is constantly expanding as a result of the Big Bang
What is red shift?
When lines in a spectrum are redder than expected - if an object has a red shift it is moving away from us
What happens 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
What can red shift be used for?
To work out the age of the universe
What is a nebula?
Swirling cloud of gas and dust
What is the life cycle of a star?
What occurs when nebula clouds are pulled together by gravity?
The spinning ball of gas starts to get hot and glows. The protostar cannot be seen because of the dust cloud
What happens to the protostar after time?
- gravity causes the star to become smaller, hotter and brighter
- after millions of years, the core temperature is hot enough for nuclear fusion to take place
- hydrogen nuclei join to form helium nuclei
- energy is released
- star continues to shine while there is enough hydrogen
What size star shines longer?
Small stars shine for longer because they have less hydrogen but use it up slower
What happens to a medium-sized star at the end?
It becomes a red giant:
- core contracts
- outer part cools
- changes from yellow to red
- expands
- gas shells, called planetary nebula, are thrown out
- core becomes a white dwarf shining very brightly but eventually cools to become a black dwarf
What happens to large stars in the end?
- become red supergiants
- core contracts
- outer part expands
- core collapses to form a neutron star (very dense)
- explosion called supernova
- remnants from supernova can merge to form a new star
- core of neutron star continues to collapse, becomes even more dense and could form a black hole
What is dangerous about a black hole?
- very large mass concentrated into a small volume
- large density
- very strong gravitational pull
