Physics Energy

The unit of energy is?

• Watt

• Kilojoule

• Kilogramme

• Volt

Complete the statement about the principal of Conservation of Energy.

Energy can be changed for one form to another but the total amount of energy

• always increases

• always decreases

• does not change

• varies according to the reaction

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Conservation of Energy Questions.

Example: A battery releases 100J of energy to a lamp. The lamp releases 80J of energy as light but it also releases heat energy. How much heat energy is released? Answer=20J ( If he total energy input is 100 and 80 is the output as light, that means that 20 J is left as heat 100J-80J=20J)..Now try these questions..

Question. A battery releases 200J of energy to a lamp. the energy is converted to heat and light. 50kJ is given out as heat. How much is released as Light?

• 100J

• 150J

• 200J

• 250J

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A Radio releases 250J of energy 10J is released as heat , How much is released as sound?

• 200J

• 220J

• 240J

• 260J

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A torch battery releases 50J of energy as heat and 240J as light, What is the total energy released from the battery?

• 250J

• 280J

• 290J

• 300J

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The % energy efficiency of an appliance is

• total energy input/ useful energy output x 100

• useful energy output /total energy input x100

• total energy input x useful energy input x100

• useful energy output /total energy input x50

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In a filament bulb the electical power input is 40W andthe light (Useful) energy output is 4W. What is the % efficiency?

• 1%

• 10%

• 0.1%

• 4%

In a modern low energy bulb, the the electrical power input is 12W and the Light (useful) power output is 4W. What is the energy efficiency of this bulb?

• 3%

• 25.5%

• 30%

• 33.3%

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look at the last two questions Suggest why modern bulbs are more efficient? (There is more than one correct answer)

• They do not need as big an energy input

• They are not as bright

• There is less wasted energy

• They release less heat.

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This one is harder.. you need to decide what is the 'useful' energy output.

A TV takes in 600J of electrical energy and gives out 300J of light, 240J of sound and 60J of heat energy (be careful here!

• 9%

• 60%

• 90%

• 85%

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