Energy Transfers Practice Questions

All four appliances are switched on for 2 minutes.

Which appliance transfers the most energy in this time?

The hairdryer is switched on at its full power rating for 4 minutes.

Calculate the energy transferred by the hairdryer.

Energy transferred = .................... J

Name the device labelled A on the diagram.

Describe the effect that device B has on the potential difference.

Give one reason why the potential difference must be reduced before the electricity reaches homes.

Work is done when charge flows in a circuit.

State what is meant by 'work is done'.

Describe the energy transfers that take place when the food mixer is switched on.

The potential difference across the motor is $230\ \mathrm{V}$ and the current in the motor is $1.3\ \mathrm{A}$.

Calculate the power transferred by the motor.

Power = .................... W

Write down the equation which links power ($P$), current ($I$) and resistance ($R$).

The current in the heating element is $5.0\ \mathrm{A}$. The resistance of the heating element is $48\ \Omega$.

Calculate the power of the heating element.

Power = .................... W

A different heating element transfers $1.8\ \mathrm{kJ}$ of energy in $2.0\ \mathrm{s}$. The current in this element is $3.0\ \mathrm{A}$.

Calculate the resistance of this heating element.

Resistance = .................... $\Omega$

During one use of the speaker, a charge of $1500\ \mathrm{C}$ flows through the circuit.

Calculate the energy transferred by the battery.

Energy transferred = .................... J

The charge of $1500\ \mathrm{C}$ flowed in a time of $25$ minutes.

Calculate the current in the circuit.

Current = .................... A

A tumble dryer has a power rating of $2.5\ \mathrm{kW}$. It is switched on for $45$ minutes.

A fridge-freezer has a power rating of $0.10\ \mathrm{kW}$. It is switched on for $24$ hours.

Determine which of the two appliances transfers more energy.

You must show your working.

Write down the equation which links power ($P$), potential difference ($V$) and current ($I$).

The microwave oven transfers $0.30\ \mathrm{MJ}$ of energy in $4.0$ minutes.

Calculate the current in the microwave oven.

Give your answer to 2 significant figures.

Current = .................... A

Calculate the energy transferred by the filament lamp when it is switched on for $3.0$ hours.

Give your answer in kJ.

Energy transferred = .................... kJ

Both lamps give out the same amount of light.

Explain why the power rating of the filament lamp is much higher than the power rating of the LED lamp.

A step-up transformer increases the potential difference to $400\,000\ \mathrm{V}$.

Calculate the current in the transmission cables.

Current = .................... A

Calculate the power wasted in the transmission cables.

Power wasted = .................... W

The same power of $500\ \mathrm{MW}$ could be transmitted through the same cables at a potential difference of $100\,000\ \mathrm{V}$.

Explain why the National Grid does not transmit electricity at this lower potential difference.

Calculate the total charge that flows from the fully charged battery before it needs recharging.

Charge = .................... C

Calculate the total energy transferred from the fully charged battery.

Energy transferred = .................... J

The motor of the scooter has a power of $400\ \mathrm{W}$.

Assume that all of the energy from the battery is transferred to the motor.

Calculate the maximum time, in minutes, that the scooter can be ridden on one full charge.

Time = .................... minutes