# PHYSICS P3

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• Created by: TJGroves
• Created on: 11-04-14 11:23
What is power?
The rate of energy transfer
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What is power usually measured in?
Watts (W) or kilowatts (kW)
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What does a power rating of 100W tell us?
It transfers 100 joules of energy every second
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What does total energy transferred depend on?
How long the appliance is on and its power rating
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What is the formula for total energy transferred?
Energy transferred = Power (W) x Time (seconds)
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What is energy usually measured in?
Joules
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What is a kilowatt-hour?
It is a UNIT of energy
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What is the formula for cost of running an appliance?
Cost = Number of kWh x cost per kWh
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What is the formula for power rating?
Power = Voltage (V) x Current (A) --> (P=VxI)
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What is better about more efficient machines?
They waste less energy and convert electrical energy at a more effective rate
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What is the formula for efficiency
Efficiency = (Energy usefully transferred/Total energy supplied)* 100%
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If a question gives you the amount of energy wasted how do you find out what the energy transferred is?
divide the smaller number by the bigger number to get and value of between 0 - 1
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What is a Sankey Diagram?
They are transformation diagrams that show what happens to energy and how much of an input energy is usefully employed and how much is wasted. The thicker the line the MORE energy it represents.
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what happens to power generated from a power station?
it is not very efficient. some is wasted via noise and heat and some when it is distributed through wires
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What is the formula for calculating the efficiency of energy transfers from a Sankey Diagram
Efficiency of Generation = electrical energy from generator/energy input from coal
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What is the formula for the efficiency of distribution
Efficiency = Useful electrical energy output/electrical energy from generator
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What is the formula for OVERALL efficiency?
Efficiency = useful electrical energy output/energy input from coal
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Provide examples of how you can reduce energy at home
cavity wall insulation/double glazing/draught proofing/hot water tank insulation/thick curtains/turning off appliances
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What is payback time?
how long it takes the money saved to match the initial cost
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Provide examples of how can you save energy in the workplace
Not printing or photocopying/recycling waste products/cycling to work/use public transport/car sharing
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Provide examples of how governments can help save energy
Grants for better insulation/trade in old boilers/improving public transport/investing in alternative energy sources/laws to make new houses more energy efficient
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Is electricity a primary or secondary energy source and explain why?
Secondary as it it derived from other energy sources
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Provide examples of non renewable energy sources
Fossil fuels e.g. coal,natural gas and oil/Nuclear energy
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Provide examples of renewable energy sources
Wind/sloar/wave/hydro electrics/biofuels/geothermal energy
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how are fossil fuels linked to environmental problems
realease CO2 when burnt which contributes to global warming and climate change/release sulfur dioxide which causes acid rain harming trees and soil/open cast mining/oil spillages
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What is nuclear energy?
Energy released from nuclear fission used to heat water creat steam and drive steam turbines
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What is the advantage of nuclear energy?
Cheap/produces a lot more energy than other sources
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What are the disadvantages of nuclear energy?
Radioactive waste/takes a long time before it can become harmless
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What are the affects of radioactive waste
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What is wind power?
the use of wind to drive propellors producing electricity through a generator
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Give examples of the advantages of wind power
clean/safe/no pollution/minimal running costs
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Give examples of the dis-advantages of wind power
Turbines can spoil the view/expensive/cannot increase power/no power when not windy
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What is solar power?
Use of solar cells to trap sunlight converting it to electricity
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Give examples of the advantages of solar power
No pollution/can be used in remote place where there is lots of sunshine and not much choice/reliable source of energy in sunny countries/still cost effective in cloudy countries/no running costs/can be small scale
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Give examples of the dis - advantages of solar power
Expensive initially and can be too expensive to link to national grid
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What is wave power?
waves provide an up and down motion to drive turbines and generator to produce electricity
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Give examples of the advantages of wave power
No pollution/no fuel costs/minimal running costs/good on a small scale
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Give examples of the dis - advantages of wave power
spoil the view/fairly unreliable waves die when wind drops/initial costs high
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What is a tidal barrage?
big dams built across river estuaries with turbines in them. The tide comes in and drives the water up several metres and drives the turbines. The source of energy is gravity of the sun and the moon
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Give examples of the advantages of a tidal barrage
no pollution/pretty reliable tides happen twice a day/good for storing energy ready for periods of peak demand/no running costs/no fuel costs/can generate large amounts of power
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Give examples of the dis - advantages of a tidal barrage
expensive/preventing free to boats/spoil the view/alter habitat/height of tide variable ie less power in spring tides/initlal costs fairly high
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What are bio - fuels?
made from plants and waste and used to gnerate electricity in thermal power stations as they are burnt to heat up water which makes steam and drives a turbine. Can be solid, liquid or gas. Can be used in cars
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Quick and natural but can destroy habitat if forests cleared to grow biofuels/can increase CO2
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Provide examples of bio fuels
straw/woodchips/ethanol
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What is geothermal energy?
The use of underground heat to create steam to drive turbines and produce electticity
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only possible where hot rocks close to the surface/free/renewable energy/no environmental problems/cost of drilling/few places where this is feasible
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What is hydroelectricity?
Flooding a valley and building a dam to allow water out through turbines to produce electricity
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advantages = immediate response to increased demand/no fuel/minimal running costs. Disadvantages = huge environmental impact/high initial costs/
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what factors need to be taken into account in comparing energy resources?
economic = running costs/set up costs: environmental = waste and air pollution/carbon dioxide/visual pollution/noise/usisng up resources/habitats/disruption of leisure activities; Efficiency of various forms
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What is electromagnetic induction?
creation of a voltage and maybe a current in a conductor by moving a magnet in or near a coil of wire changing the magnetic field and creating a voltage and a current flows through the wire (if the circuit is complete)
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How do generators work?
They use electromagnetic induction to turn kinetic energy from turbines into electricity
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How do you create a bigger voltage?
Turn the magnet faster
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What is the impact of this?
you need more power from a primary energy source to do this e.g. coal. The bigger the current and voltage the more fuel we use up
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What is the national grid?
network of pylons and cables covering the UK taking electricity into homes and factories. Power can be gnerated anywhere on the grid and fed into it
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what is the advantage of using a high voltage rather than a high current
A high current loses lot energy as heat in wires. A high voltage chaeaper more efficient as low current and low energy loss.
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What happens to the voltage when it reaches our homes?
It is reduced
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## Other cards in this set

### Card 2

#### Front

What is power usually measured in?

#### Back

Watts (W) or kilowatts (kW)

### Card 3

#### Front

What does a power rating of 100W tell us?

### Card 4

#### Front

What does total energy transferred depend on?

### Card 5

#### Front

What is the formula for total energy transferred?