Energy Transfers in Circuits Practice Questions

State what is meant by the power of a device.

Calculate the power of the energy transfer from the power bank to the phone.

power = ............................................... W

Which statement describes the main energy transfer when the fan is switched on?

Put a cross ( ☒ ) in the box next to your answer.

☐ A from the thermal store of the battery to the kinetic store of the fan blades

☐ B from the chemical store of the battery to the kinetic store of the fan blades

☐ C from the kinetic store of the battery to the chemical store of the fan blades

☐ D from the chemical store of the fan blades to the thermal store of the battery

Calculate the power supplied to the fan motor.

power = ............................................... W

After the fan has been running for some time, the motor and the connecting wires feel warm.

State why some of the energy supplied by the battery is transferred to the thermal store of the surroundings.

Calculate the energy transferred from the battery in the $12$ minutes.
Give your answer in kJ.
Use an equation selected from the list of equations at the end of the paper.

energy transferred = ............................................... kJ

The connecting wires inside the drill are made from thick copper wire.

Explain how this reduces the unwanted energy transfer inside the drill.

Calculate the power dissipated by the resistor.
Give your answer to two significant figures.

power = ............................................... W

Explain, in terms of electrons and the lattice, why the temperature of the resistor increases when there is a current in it.

When there is an electric current in a component, there is a heating effect.

A student says:

"The heating effect of an electric current is always a problem and should be avoided."

Evaluate this statement. In your answer you should refer to domestic electrical devices.

Calculate the current in the car kettle when it is working normally.

current = ............................................... A

A kitchen kettle has a power rating of $2300\ \mathrm{W}$ and is connected to the $230\ \mathrm{V}$ mains supply. The current in the kitchen kettle is $10\ \mathrm{A}$.

Explain why the car kettle has a larger current in it than the kitchen kettle, even though its power rating is much lower.

State what is meant by a power rating of $900\ \mathrm{W}$.

Calculate the energy transferred by the microwave oven in the $6$ minutes.
Give your answer in kJ.

energy transferred = ............................................... kJ

The slow cooker has a much lower power rating than the microwave oven.

Use a calculation to show which of the two appliances transfers more energy during the times given in the table.

An electric workshop heater is connected to a wall socket using an extension cable. The current in the heater is $12\ \mathrm{A}$.

The workshop has two extension cables:

• cable A has a resistance of $0.50\ \Omega$
• cable B has a resistance of $0.20\ \Omega$

The current in the heater is $12\ \mathrm{A}$ with either cable.

Calculate how much less energy is wasted in cable B than in cable A when the heater is used for $30$ minutes.
Give your answer in kJ.

energy = ............................................... kJ