Physics P1 2.4 Energy and efficiency.

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What is the efficiency of an appliance equal to?
Useful energy transferred by the appliance/(divided by) the total energy supplied to the appliance (x100%).
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What is energy measured in?
Joules (J).
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What unit is used to measure all forms of energy?
Joules (J).
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What is the energy supplied to a machine often called?
The input energy.
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What do we know, from the conservation of energy, that the input energy (energy supplied) is equal to?
Useful energy transferred + energy wasted.
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If a machine wastes less energy, what would the machine be deemed to be?
More efficient.
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What equation can we use to calculate the efficiency of any appliance that transfers energy?
Efficiency = useful energy transferred by the appliance (over/divided by) the total energy supplied to the appliance (x100)
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How can the efficiency be shown?
It can be left as a fraction or multiplied by 100 to give a percentage.
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How is an electric heater different from all other appliances in relation to energy efficiency?
No appliance can be 100% efficient, except for an electric heater which usually transfers all of the electrical energy supplied to it by heating its surroundings.
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How can the energy transfer through an appliance be represented?
With a Sankey diagram.
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What do the measures to make machines more efficient include?
Reducing friction, air resistance, electrical resistance and noise due to vibrations.
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In a light bulb, for every 25 joules of energy that are supplied to the bulb, 5 joules are usefully transferred into light energy. What is the efficiency of the bulb?
The efficiency is 0.2 or 20%.
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A machine is adjusted so that it wastes less energy because of friction. What happens to the efficiency of the machine?
The efficiency increases.
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No appliance can be more than 100% efficient therefore what should an efficiency calculation never be more than?
1 or 100%, if it is greater then you have made an error in your workings out.
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Efficiency is a ratio, therefore what doesn't it have?
A unit.
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**LOOK UP SANKEY DIAGRAMS**
**LOOK UP SANKEY DIAGRAMS**
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Card 2

Front

What is energy measured in?

Back

Joules (J).

Card 3

Front

What unit is used to measure all forms of energy?

Back

Preview of the front of card 3

Card 4

Front

What is the energy supplied to a machine often called?

Back

Preview of the front of card 4

Card 5

Front

What do we know, from the conservation of energy, that the input energy (energy supplied) is equal to?

Back

Preview of the front of card 5
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