Lesson test: Power and energy in a circuit

1.[2p]
Electrical power is voltage times current because

voltage is energy per charge and current is charge per time, so their product is energy per time

Correct

power is always equal to the resistance

The answer is: voltage is energy per charge and current is charge per time, so their product is energy per time

current cancels the voltage

The answer is: voltage is energy per charge and current is charge per time, so their product is energy per time

power is measured in coulombs

The answer is: voltage is energy per charge and current is charge per time, so their product is energy per time

4.[3p]
Heat dissipated in a resistance grows with the square of the current, which is why

current, not voltage, is what melts wires, and grids transmit power at high voltage and low current

Correct

voltage is more dangerous than current

The answer is: current, not voltage, is what melts wires, and grids transmit power at high voltage and low current

doubling the current doubles the heat

The answer is: current, not voltage, is what melts wires, and grids transmit power at high voltage and low current

a thin wire is cooler than a thick one

The answer is: current, not voltage, is what melts wires, and grids transmit power at high voltage and low current

5.[2p]
A 2000 W kettle runs for 4 minutes. How much energy does it use, in kilowatt-hours? Give three decimal places.

CorrectNot quite: 0.133

6.[1p]
The kilowatt-hour is a unit of

energy

Correct

power

The answer is: energy

current

The answer is: energy

voltage

The answer is: energy

7.[2p]
A motor that draws 100 W and delivers 85 W of mechanical output

is 85 per cent efficient, with the missing 15 W lost as heat

Correct

is 100 per cent efficient

The answer is: is 85 per cent efficient, with the missing 15 W lost as heat

delivers more power than it draws

The answer is: is 85 per cent efficient, with the missing 15 W lost as heat

stores the extra 15 W

The answer is: is 85 per cent efficient, with the missing 15 W lost as heat

Sign in

Power and energy in a circuit

1.[2p]
Electrical power is voltage times current because

2.[1p]
A resistor carries 0.5 A with 6 V across it. What power, in watts, does it dissipate?

3.[2p]
A 100 ohm resistor has 10 V across it. What power does it dissipate, in watts?

4.[3p]
Heat dissipated in a resistance grows with the square of the current, which is why

5.[2p]
A 2000 W kettle runs for 4 minutes. How much energy does it use, in kilowatt-hours? Give three decimal places.

6.[1p]
The kilowatt-hour is a unit of

7.[2p]
A motor that draws 100 W and delivers 85 W of mechanical output

1.[2p] Electrical power is voltage times current because

2.[1p] A resistor carries 0.5 A with 6 V across it. What power, in watts, does it dissipate?

3.[2p] A 100 ohm resistor has 10 V across it. What power does it dissipate, in watts?

4.[3p] Heat dissipated in a resistance grows with the square of the current, which is why

5.[2p] A 2000 W kettle runs for 4 minutes. How much energy does it use, in kilowatt-hours? Give three decimal places.

6.[1p] The kilowatt-hour is a unit of

7.[2p] A motor that draws 100 W and delivers 85 W of mechanical output

1.[2p]
Electrical power is voltage times current because

2.[1p]
A resistor carries 0.5 A with 6 V across it. What power, in watts, does it dissipate?

3.[2p]
A 100 ohm resistor has 10 V across it. What power does it dissipate, in watts?

4.[3p]
Heat dissipated in a resistance grows with the square of the current, which is why

5.[2p]
A 2000 W kettle runs for 4 minutes. How much energy does it use, in kilowatt-hours? Give three decimal places.

6.[1p]
The kilowatt-hour is a unit of

7.[2p]
A motor that draws 100 W and delivers 85 W of mechanical output