# GCSE p1b - calculating efficiency

GCSE p1b - calculating efficiency work booklet

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- Created on: 23-06-09 11:57

First 224 words of the document:

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.

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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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