Flashcards in P2 Deck (70):
What are photocells and how do they work?
- photocells absorb light energy from the sun on flat silicon surfaces, causing electrons to be knocked loose from the silicon atoms in the crystal. The electrons flow freely, called an electrical current
What does the power of a photocell depend on?
- the surface area exposed to light
- the intensity of the light
- the distance between the light and the photocell
What must be done to maximise the power output of a photocell?
- an efficient solar collector must track the position of the sun in the sky
What are the advantages of photocells?
- they use renewable energy from the sun
- need no fuel
- no pollution or waste is formed
- little maintenance is needed
- have a long life
- can operate in remote locations
What are the dissadvantages of ohotocells?
- no power at night or during bad weather
- expensive to buy
- take up a lot of space
What is passive solar heating?
- caused by visible light and infrared radiation passing through glass into a room
- the light and infrared is absorbed by objects causing them to heat up
- the objects then re-emit infrared of longer wavelength, which reflects off the glass to heat up the room
What is an example of a convection current?
What are the advantages of wind turbines?
- renewable energy source
- no chemical pollution or waste
- it is free after set up costs
What are the disadvantages if wind turbines?
- require a large amount of space
- dependent on wind
- visual pollution
What is the Dynamo effect?
- a way in which electricity can be generated by:
> moving a wire, or coil of wire near a magnet
> moving a magnet near a wire or coil of wire
- the wire cuts through the lines of force in the magnetic field and a current is produced by electromagnetic induction
How can more current be generated in the Dynamo effect?
- stronger magnets
- more turns in the coil
- moving coil or magnet faster
What happens in an AC generator?
- a coil of wire is rotated in a magnetic field
- as the coil cuts through the magnetic field the relative motion causes a current to be generated in the coil
What happens to the current in an AC generator?
- it alternates, it reverses it's direction of flow, every half turn, so an Alternating current is produced
How is electricity produced in a power station?
1- the fuel is burned to release heat energy
2- the heat boils the water which produces steam
3- the steam powers the turbine, which drive the generators
4- the generators produce electricity
How can you calculate the efficiency of power stations?
(Electrical energy output➗fuel energy input) ✖️100
Name 3 greenhouse gases?
- carbon dioxide
- water vapour
State 4 pieces of evidence that suggests humans influence on global warming?
- humans burning more fossil fuels
- the amount of carbon dioxide in the atmosphere is increasing
- green house gasses trap in heat and prevent it from escaping
- the earths temperature is increasing
State 4 pieces of evidence which suggests natural causes of global warming?
- the temperature of the earth changes over time
- the increase of carbon dioxide is not significant enough to affect global temperatures
- water vapour has a much more significant effect on global warming
- the temperature of mercury and Venus have increased
What is the greenhouse effect?
- occurs because short wavelength electromagnetic radiation from the sun is absorbed by the earth causing it to heat up.
- the Earth then radiates heat as longer wavelength infrared radiation.
- greenhouse gases absorb some of theses longer wavelength infrared waves, warming the atmosphere
Name 3 fossil fuels?
- crude oil
- natural gases
How is energy released from fossil fuels ?
- fuel is burned to release heat energy
Name 3 types of Biomass?
How is energy released from biomass?
- biomass is fermented to generate methane
Name a nuclear fuel?
How is energy released from nuclear fuels ?
- fuel rods release heat energyn
What do transformers do?
- used to increase and decrease the voltage before and after transmission.
- the voltage is too high for consumers so transformers are used to reduce the voltage for a cafe use
What is Economy-7?
- when companies offer an off peak rate for 7 hours a night, as demand at night is lower
What are the advantages for Economy-7?
- less demand at night
- cheaper for consumers
- avoids waste of electrical energy
What are the disadvantages of Economy-7?
- inconvenient to run appliances at night due to noise
What are the advantages of fossil fuels?
- cheap and easy to obtain
- enough reserves for a short to medium time
- coal, oil and gas fired power stations are flexible in meeting demands
- burning gas does not produce SO2
What are the advantages of Biomass?
- it is renewable
What are the advantages of Nuclear fuel?
- cost and rate of fuel production is quite low
- can be situated in sparsely populated areas
- flexible on meeting demands
- doesn't produce CO2 or SO2
- high stocks of fuel
- reduce use of fossil fuels
What are the advantages of renewable sources of energy?
- produce clean electricity
- can be constructed in remote areas
- no fuel cost
- no chemical pollution
- low maintenance
- no global warming produced
What are the disadvantages of using fossil fuels?
- produces CO2 and SO2
- removing SO2 adds to costs
- oil is transported, leading to risks of spillage and pollution
- expensive forms of transport
What are the disadvantages of using Biomass?
- produces CO2 and SO2
- large area need to grow trees
What are the disadvantages of using nuclear fuel?
- radioactive material is very dangerous and stays that for thousands of years
- storing radioactive waste is very expensive
- building and decommissioning nuclear power stations are costly processes
- long start up time
- high maintenance costs
What are the disadvantages of using renewable sources?
- often don't produce much electricity
- take up lots of space
- mostly unreliable
- high initial capital outlay
How can you calculate the power of an appliance?
Power= current ✖️ voltage
How can you calculate the cost if running an appliance?
Total cost =
Number of kilowatt hours used ✖️ cost per unit
What us a kilowatt hour?
A measurement of how much energy has been used
How do you calculate the amount of energy supplied?
Energy supplied= power ✖️ time
What are radioactive materials?
- substances that give out nuclear radiation all the time
Name the three types of nuclear radiation?
Name the characteristics of Alpha radiation?
- absorbed by a few CM of air or thin paper
Name the characteristics of Beta radiation?
- MEDIUM STRENGTH
- passes through air and paper, absorbed by a few mm of aluminium
Name the characteristics of Gamma radiation?
- very penetrating, needs many cm of lead or meters of concordat to stop it
What are the uses of Alpha radiation?
- smoke detectors
> the emitted particles ionise air particles and the ions formed are attracts to the oppositely charges electrodes.
>when smoke enters the space the alpha particles are absorbed by the smoke particles a smaller current then flows which starts the alarm
What are the uses of Beta radiation?
- Paper thickness gauge
> when beta radiation passes Through paper, some of it is absorbed
> if the papers thickness is too great, more beta rays will be absorbed and less pass to the detector, indicating that the paper is too thick
What are the uses of Gamma radiation?
- cancer treatment
- destroys cancerous cells
How is radioactive waste disposed of?
- low level waste is sealed and buried on landfill
- higher level waste is enclosed in glass and stored underground in steel cylinders
What are black holes?
- dense, dying stars with a strong gravitational field
- have a very large mass concentrated into a small space
- nothing can escape a black hole, not even light
What information can probes send to earth about another planet?
- magnetic fields
- radiation levels
- surrounding landscape
What are the advantages of using probes to investigate planets?
- costs are lower as there is no need for human supplies
- safety isn't an issue
What are the disadvantages of using probes to investigate planets?
- reliability has to be high as there is no one to fix any breakdowns
- instruments must require zero maintenance
What are asteroids?
- rocks left over from the formation of the solar system
- normally orbit the sun in a belt between Mars and Jupiter but occasionally they get knocked of and head towards earth
What could happen if an asteroid hit earth?
- an impact would create a crater, which could trigger the ejection of hot rocks
- the heat may cause widespread fires
- sunlight could be blocked out by the dust from an explosion
- it could trigger a climate change
- whole species could become extinct
What evidence is there to suggest that asteroids have collided with earth many times in the past?
- craters can be found all over the planet
- there are layers of unusual elements found in rocks
- there are sudden changes in the number of fossils found in adjacent rock layers, which could be due to the sudden death of many animals
What happens when asteroids in the belt bump into eachother?
- they can join up or shatter.
- they can't combine to form a new planet because the larger mass formed feels a greater pull from jupiter's strong gravitational field And is attracted to it and breaks up
What are Comets and what are their characteristics?
- a small body with a core of frozen gas (ice) and dust.
- the characteristics tail is a trail of debris.
- comets come from the objects that orbit the sun.
- they have highly elliptical orbits around the sun
- the speed of the comet increases as it approaches the sun
Why does the speed that a comet is traveling increase as it approaches the sun?
- the comet's speed increases as a result of the increase in the strength of gravity as it approaches the sun.
What is a NEO?
- a near earth object, an asteroid or comet that is on a possible collision with earth
what actions are taken to protect the human race from large NEOs?
- survey the skies with telescope to identify likely NEOs as early as possible
- monitor large object's progress with satellites
- deflect the object with an explosion if a collision is likely
What can we observe from looking at the stars?
- nearly all the galaxies are moving away from us
- distant galaxies are moving away more quickly
- microwaves radiation is received from all parts of the universe
What is Red shift?
- the shifting of the wavelengths of light towards the red end of the spectrum.
- it can be observed in the light we receive from galaxies, the further away the galaxy, the greater the Red shift
When is a proto-star formed ?
- when interstellar gas clouds collapse under gravitational attraction.
- then thermonuclear fusion reactions take place, releasing massive amounts of energy and increasing the star's temperature.
- during this time, the star experiences a long period of normal life.
- eventually, the supply of hydrogen runs out, causing the end of the star.
What does the lifespan of a star depend on?
- the star's supply of oxygen
Describe the end stages of a heavy-weight star?
1- star swells up to form a RED SUPERGIANT
2- the red supergiant rapidly shrinks and explodes, releasing massive amounts of energy, dust and gas into space . This is a SUPERNOVA
3- the next stage depends on the size of the star:
> the remnants of stars up to ten times the mass of the sun form a NEUTRON STAR, which is made of very dense matter.
> stars greater than ten times the mass of our star leave behind BLACK HOLES.
Describe the end stages of a medium-weight star?
1- star swells to form a RED GIANT
2- the core of the red giant contracts (shrinks) to be surrounded by outer shells of gas (planetary nebula)
3- the core cools and contracts to become a WHITE DWARF, with a density thousands of times greater than any matter on Earth
What was the Ptolemaic model of the universe?
- stated that the Earth was the centre of the universe, and that the Earth was surrounded by Crystal spheres which held the other planets and stars