Topic Menu

Cyber-chess a chess instruction site

GCSE Standard Questions: Electricity in the Home

Q14. The photo shows a person using an electric lawn mower.

(a) The lawn mower is connected to the mains electricity supply. What is the frequency of the mains electricity supply in the UK?

50 Hz

[2 marks]

(b) The lawn mower has a switch on each side of the handle. Here is the circuit diagram for the lawn mower.

The motor in the lawn mower can only be turned on when the person using it holds the handle of the lawn mower with both hands. Explain why.

For safety reasons two hands have to be on the handle. To ensure that is the case, both switches need to be closed to complete the series circuit and allow charge to flow so that there is a current in the circuit.

[2 marks]

(c) The power input to the motor is 1.8 kW The resistance of the motor is 32 Ω.

Calculate the current in the motor.

P = IV but V = IR

so, P = I(IR) = I2R

I2 = P/R

P = 1.8 kW = 1800 W

I2 = 1800/32 = 56.25

I = √56.26

I = 7.5 A

[4 marks]

(d) The useful power output from the motor is 1.5 kW

Calculate the time it takes for the motor to transfer 450,000 J of useful energy.

P = E/t

P = 1.5 kW = 1500 J/s

t = E/P = 450,000/1500 = 300s

300s = 5 minutes

[3 marks]

(Total 11 marks)