# Physics P1 3.2 Electrical power.

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What the power of an appliance?
The power of an appliance is rate of transfer of energy per second.
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What is the equation to work out power?
P = E (over/divided by) t.
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What does the P stand for in the equation for power?
P is the power in watts (W).
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What does the E stand for in the equation for power?
E is the energy in joules (J).
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What does the t stand for in the equation for power?
t is the time taken (in seconds) for energy to be transferred.
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What is the equation for efficiency?
Efficiency = useful power out (over/divided by) total power in (x100).
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What is the unit that power is measured in?
Watt (W).
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How many joules of electrical energy is transferred to other forms of energy in one second by 1 watt of power?
1 joule.
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Wh is power usually given in kilowatts (kW)?
Often a watt is too small a unit to be useful, 1 kilowatt = 1000 watts.
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How many watts are equivalent to 12 kilowatts?
12000W.
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An electric motor transfers 49kJ of electrical energy into kinetic energy in 2 minutes. What is the useful power output of the motor?
400W
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**BE SURE THAT YOU PRACTICE EFFICIENCY CALCULATIONS USING BOTH FRACTIONS AND PERCENTAGES**
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## Other cards in this set

### Card 2

#### Front

What is the equation to work out power?

#### Back

P = E (over/divided by) t.

### Card 3

#### Front

What does the P stand for in the equation for power?

### Card 4

#### Front

What does the E stand for in the equation for power?

### Card 5

#### Front

What does the t stand for in the equation for power?