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P7: Quiz 13 – Answers

P7: Quiz 13 – Answers

1)

a) Power is a rate of energy transfer (or the rate of energy transfer per second)

b) 1 watt is 1 joule of energy transferred per second

c) power = potential difference x current, or P = VI

Power is measured in watts (W), potential difference is measured in volts (V) and current is measured in amps (A)

2)

a) 24 W

b) 7,200 J

3)

a) 2,300 W

b) 2,760 KJ

4)

a) P = VI, or power = potential difference x current

b) V = IR, or potential difference = current x resistance

c) P = I^{2}R, or power = current^{2} x resistance

5)

a) 288 W

b) 69,120 J

6)

a) 2,300 W

b) 23 Ω

**Questions**

1)

a) What is power?

b) Power is measured in watts; what is 1 watt is other units?

c) Write the equation that links power, current and resistance. Give the units for each of the variables. Also, write down the formula triangle.

2) A filament bulb in an electric circuit has a current passing through it of 4 A and a potential difference across it of 6 V.

a) Work out the power of the filament bulb.

b) Calculate how much energy will be transferred to the bulb if the bulb was on for 5 minutes.

3) A washing machine is plugged into the mains electricity of a house. It has a current of 10 A.

a) Calculate the power of the washing machine.

b) Calculate the energy transfer when the washing machine is on for a quick 20-minute wash. Give your answer in kilojoules.

4) You do not need to include the units for the sub parts in this question.

a) Write down the power formula that connects power, potential difference and current.

b) Write down the equation that links potential difference, current and resistance.

c) Write down the power equation that does not contain potential difference (sub in the potential difference from part b into part a to eliminate potential difference from the formula).

5) A device has a resistance of 8 Ω and a current of 6 A.

a) Calculate the power of the device.

b) Calculate the energy transfer when the device is on for 4 minutes. Give your answer in joules.

6) A device that is connected to the mains has a current of 10 A passing through it.

a) Calculate the power of the device.

b) Calculate the resistance of the device.