P2 Flashcards
How do photocells work?
- The sun’s energy is absorbed by the photocell
- Electrons are knocked loose
- The electrons flow to produce an electric current
What are the advantages and disadvantages of photocells?
Advantages: Use renewable energy, no need for fuel, no pollutions or waste, little maintenance, long life, operate in remote locations (no need to install power cables).
Disadvantages: No power unless sun is shining, expensive, take up space.
How can the sun’s energy be used?
Photocells, curved mirror to focus the Sun’s light and make it more intense, passive solar heating and it produces convection currents that can be transformed into energy by using wind turbines.
What is passive solar heating?
Glass is transparent to radiation from the sun so passive solar heating is where visible light and infrared radiation are absorbed by objects in the room, causing them to heat up and re-emit radiation of a longer wavelength so it can’t travel through the glass and is reflected back into the room, causing it to be heated up.
What are the advantages and disadvantages of wind turbines?
Advantages: renewable, no chemical pollution or waste, free after set up costs.
Disadvantages: lots of space needed, dependent on wind, cause visual pollution.
What is the dynamo effect?
The way electricity can be generated by moving a (coil of) wire near a magnet or visa versa. When this happens, the wire cuts through the lines of force of the magnetic field so a current is produced by electromagnetic induction in the wire, if part of a complete circuit.
How can you increase the current produced in the dynamo effect?
- Stronger magnets
- More turns in the coil of wire
- Moving the coil faster
- Moving the magnet faster
What is an AC generator and how does it work? (+ what is AC frequency?)
Coil of wire rotated in a magnetic field (magnetic and wire are close)
Coil cuts through magnetic field, relative motion causes a current to be generated by relative motion
The current alternates (reverses direction of flow every half turn of coil) so an alternating current is produced
The frequency of AC electricity is the number of cycles per second (picture it on a graph - one peak and one trough)
How is electricity produced in power stations?
- Fuel is burned to release heat energy
- Heat boils the water to produce steam
- The steam drives the turbines, which drive generators
- The generators produce electricity
- Distributed on power lines (national grid)
How can you work out the efficiency of a power station?
Electrical energy output
——————————— x 100
Fuel energy input
What is the supporting and refuting evidence of global warming?
Supports: Humans are burning more fossil fuels, CO2 in atmosphere is increasing, greenhouse gases do trap heat, average planet temp is increasing.
Refutes: Earth’s temperature fluctuates in a 40000 year cycle, increase in CO2 is very small, water vapour more significant than CO2, surface temps of Mercury and Venus have also increased
What is the greenhouse effect?
It occurs because short wavelength electromagnetic radiation from the sun is absorbed by earth, causing it to heat up and re-emit radiation of a longer wavelength which can be absorbed by greenhouse gases, warming the atmosphere.
Give examples of fossil fuels
- Crude oil
- Coal
- Natural gas
Give examples of biomass fuels and how they are used
Wood
Straw
Manure
Fermented to generate methane
What voltage is electricity transmitted at and why?
40000V to reduce heat loss and costs - an electric current is transmitted along a wire, the wire heats up due to collisions in the material so the wire looses energy by heat.
Make a table for the advantages and disadvantages of each energy source (fossil fuels, biomass, nuclear and renewable)
Check in revision guide page 29
How do you work out power? (Include units)
Power (watts) = current (amps) x voltage (volts)
How do you work out the cost of using an appliance?
Number of kWh x cost per unit
How do you work out energy supplied?
Power (kW) x time (h)
What is radioactivity?
It involves a change in the structure of the radioactive atom and the release of one or more of the three types of nuclear radiation
How can you use alpha radiation?
Smoke detectors (americium-241): alpha particles ionise air particles. The ions are attracted to the oppositely charged electrodes, producing a current in the circuit. When smoke entered the space between the two electrodes, less ionisation takes place because alpha particles are absorbed by smoke particles = smaller current = alarm
What are the uses of beta radiation?
Tracers - small amount of radioactivity put into a system so its progress can be followed by a tracker (like how nitrogen moves through a plant)
Paper thickness gauge - some beta radiation is absorbed, if less is detected then the thickness of paper must be reduced
What are the uses of gamma radiation?
Treat cancer - destroys cancerous cells. Must be careful not to destroy living cells.
Sterilise equipment
Non-destructive tests can be carried out on welds
Name three difficulties of manned space travel
- takes a long time
- fuel required takes up lots of room
- room needed for water and oxygen
- stable atmosphere needed
- low gravity effects health
- need shielding from cosmic rays
Briefly explain what evidence there is for the Big Bang
Nearly all galaxies are moving away from us
Distant galaxies are moving quicker
Microwave radiation is received from all parts of the universe
How is a protostar formed?
When interstellar gas clouds collapse under gravitational attraction, then thermonuclear fusion reactions take place, releasing energy.
Briefly explain the red shift
Shifting of wavelengths of light towards the red spectrum. The further away the galaxy, the greater the red shift; evidence for the expansion of the universe.
What are the stages of a heavy weight star?
Interstellar gas cloud -> protostar -> main sequence star -> red supergiant -> supernova -> neutron star (up to x10 the size of the sun) or black hole (over x10 the size of the sun)
What are the stages of a medium weight star?
Interstellar gas cloud -> protostar -> main sequence star -> red giant -> planetary nebula -> white dwarf
What is the Ptolemaic model of the universe?
Geocentric
Surrounded by crystal spheres which held other planets and stars
What is the Copernicus model of the universe?
16th century, copernicus
Planets sat on spheres, a fixed distance from the sun
Stars were fixed on the outmost sphere and didn’t move
Sun is centre of the universe
Earth rotated every 24 hours
Earth takes a year to revolve around the sun
What did Galileo discover?
He used telescopes to observe the moon’s surface and saw it wasn’t a perfect sphere.
Four moons orbiting Jupiter
Venus has phases like the moon so it couldn’t be attached to a crystal sphere but it orbited the sun like earth.
