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GCSE Standard Questions: Electricity in the Home

Q19. The photo shows an electric car being recharged.

(a) The charging station applies a direct potential difference across the battery of the car.

What does 'direct' potential difference mean?

The polarity of the supply does not change - one terminal is permanently positive in polarity with respect to the other one.

Direct potential difference results in direct current flow. An AC supply has the terminals continually changing polarity with respect to each other and produces an alternating current flow.

[1 mark]

(b) The battery in the electric car can store 162 MJ of energy.

The charging station has a power output of 7.2 kW.

Calculate the time taken to fully recharge the battery from zero.

162 MJ = 162 x 106 J

7.2 kW = 7200 W

power = energy/time

P = E/t

t = E/P

t = 162 x 106/7200

t = 22500 s

t = 375 minutes

t = 6 hours 15 minutes

[5 marks]

(c) The potential difference applied across the battery from the charging station is 480 V.

There is a current of 15 A in the circuit connecting the battery to the motor of the electric car.

Calculate the resistance of the motor.

V = IR

R = V/I

R = 480/15

R = 32 Ω

[4 marks]

(d) Different charging systems use different electrical currents.

Charging system A has a current of 13 A.

Charging system B has a current of 26 A.

The potential difference of both charging systems is 230 V.

 

Tick the box that correctly compares the time taken to recharge a battery using charging system A with the time taken using charging system B.

Time taken using system A is half the time of system B  
Time taken using system A is the same as system B  
Time taken using system A is double the time of system B

[1 mark]

(Total 11 marks)