Energy,electricity and fuels Flashcards
Negatives of photocells
Expensive to buy
No power at night or in bad weather
How do photocells work
What does the power of the photocell depend on
Sun’s energy is absorbed causing electrons to be knocked loose from silicon crystals
These electrons flow freely as ELECTRIC CURRENT charge
It transfers light energy into an electric DC current
Why are photocells good for capturing maximum light energy
How can they be used to capture more sunlight
What current to they use
Photocells have a flat surface
They can be joined together to create larger surface area, more energy
Photocells use DC current that travels in the same direction all the time
What does power output of photocell depend on
Power output depends on light intensity,surface area and distance from light source
How can solar panels be used to heat water for washing and heating buildings
Sunlight absorbed by panel transfers to heat energy
Water passed over this heats up
Positives of photocells
Little maintainance Operate in remote locations No fuel or power cables Uses renewable energy source No pollution or waste
What can glass provide for heating buildings
Passive solar heating, this traps sun energy but won’t distribute or change it into another form of energy
Curved mirror
Focuses sunlight to heat up a solar panel
How do windows heat up rooms
Light passes straight through windows
It is absorbed by objects in the room
They emit infrared radiation (longer wavelength than visible light) which is reflected back into the room by the glass so cant escape
Room warms up
Solar collector and why is it used
A solar collector can track the sun to maximise power output
requires extra technology and therefore cost
Why can light pass straight through glass
Glass is transparent to some wavelengths of sun’s radiation,including visible light so light passes straight through glass windows
How is energy generated in a dynamo
What kind of circuit is this
By moving a wire near a magnet/ magnet near a wire
The wire cuts through the lines of force of the magnetic field and a current is produced in the wire
This is a complete circuit
How can you increase current produced in a dynamo
A stronger magnet
Moving wire/magnet faster
Adding more turns of wire on the coil
How do wind turbines work
Sun heats the air producing convection currents-wind
They turn the turbines
Turbines transfer kinetic energy into electrical energy
Positives and negatives of wind turbines
Renewable energy source
No chemical pollution or waste
Needs space and windy region
Dependant on wind
Visual pollution due to size
Why do generators use the dynamo effect
Generators produce alternating current AC
so direction of current is continually alternating every time magnet/coil changes direction
Batteries produce DC
Generators produce an Alternating Current
Describe this
The direction of the current continually alternates, every time the magnet or coil changes direction
The voltage generated changes direction causing current to change direction
What do consumers access electricity through
The national grid
How do fossil fuels being burnt produce electricity in the national grid
Fossil fuels are burned to release heat energy Heat energy boils water to produce steam Steam rotates turbines Turbines turn generators Electricity is produced
How is producing electricity for the national grid different to a nuclear power station
Fuel rods of uranium release energy as heat to make steam in the power station
How can biomass be used to produce electricity
Biomass eg. wood can be burned or fermented to generate methane
Methane can be burned in the power station
The biomass absorbs carbon dioxide then releases it when burnt
Biomass needs lots of land
What is electric current
Flow of electric charge, transfers energy from power supply to the components in the circuit
What are Watts
1 watt is the transfer of 1J of energy per second
What is off peak electric
A company can sell the electricity they generate so they don’t have to turn off power stations
For the user off peak is more economical
For producer off peak is less economical
What can off-peak electricity be used for
Heating water and storage heaters
Powers washing machines and dishwashers at night
The number of units of electricity used by appliances depends on
Power rating in kilowatts
Time in hours it is switched on for
How do you calculate the cost of using a device
kWh
Number of kilowatt hours (kWh)= power rating(kW) X time (h)
Total cost= number of kW hours(kWh) X cost of one kWh
What is current fed through (in the National grid) to supply electricity to homes efficiently with electricity
What does this do
Transformers change voltage of alternating currents
They increase voltage of supply and at the same time, reduce current
Increasing voltage reduces energy lost as heat (through heating) during electricity transmission, so reduces costs
Batteries and photocells produce an Direct Current
Describe this
Electric current flowing in only one direction
