GCSE p1b - calculating efficiency

GCSE p1b - calculating efficiency work booklet

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  • Created on: 23-06-09 11:57
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Calculating Efficiency.
Efficiency (%) = Useful Energy Out x 100
Total Energy In
Questions
1) A light bulb takes in 30J of energy per second. It transfers 3J as
useful light energy and 27J as heat energy. Calculate the efficiency.
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2) A kettle takes in 2000J of energy per second. It transfers 1500J
as useful heat energy and 500J is wasted as sound energy. Calculate
the efficiency of the kettle.
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Remember: In the exam they may not ask for efficiency
as a percentage!!!
3) Calculate the efficiency of a hair dryer which takes in 3000J of
energy per second and transfers 600J as useful heat energy.
Express your answer as a decimal and not as a percentage.
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__________________________________________________
4) Calculate the efficiency of a TV which takes in 5000J of energy per
second and transfers 1000J as useful light energy and 1500J as
useful sound energy. The remaining 2500J is wasted as heat energy.
Express your answer as a decimal and not a percentage.
__________________________________________________
__________________________________________________
Electrical Devices.
Power = energy transferred / seconds
Power is measured in W (Watts) or kW (kilowatts)
1) Calculate the power of a drill which transfers 2000J of energy in 5
seconds. Show your answer in watts and kilowatts.
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Convert the following powers into kilowatts
a) 3000W _________________________________
b) 20W ___________________________________
c) 900W __________________________________
d) 20000W ________________________________
e) 1W ____________________________________
energy transferred = power x time
(kilowatthour, kWh) (kilowatt, kW) (hour, h)
Remember: When calculating energy transferred; power
MUST be in kW and time MUST be in hours!!!
3) Calculate the energy transferred by a computer with a power of
2kW which is left on for 1 hour.…read more

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Radiation
1) Radiation can travel through a vacuum; what is a vacuum?
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2) What kind of surface emits the most thermal radiation?
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3) What kind of surface reflects the most thermal radiation?
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4) What kind of surface absorbs the most thermal radiation?
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Payback Time
1) Fill in the payback time in the table.
REMEMBER: 0.…read more

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Generating Electricity
A renewable energy source is one which will not run out and is
continually being replaced
A nonrenewable energy source is one which will run out and cannot be
replaced
1) Give three examples of fossil fuels?
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2) Which non-renewable energy source does not contribute to the
greenhouse effect? ___________________________________
3) Is wood renewable or non-renewable? Explain your answer.
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4) Explain how a coal fired power station works.…read more

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