Figure 1 shows an electric car being recharged.
i- The charging station applies a direct potential difference across the battery of the car.
What does ‘direct potential difference’ mean?
[1 mark]
ANSWER
The potential difference is the potential difference which always remain same and causes current to flow in the same direction, provided that the polarity of the battery remains unchanged.
ii- Which equation links energy transferred (E), power (P) and time (t)?
[1 mark]
ANSWER
iii- The battery in the electric car can store 162 000 000 J of energy.
The charging station has a power output of 7200 W.
Calculate the time taken to fully recharge the battery from zero.
[3 marks]
SOLUTION
iv- Which equation links current (I), potential difference (V) and resistance (R)?
[1 mark]
SOLUTION
v- The potential difference across the battery 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.
[3 marks]
SOLUTION
vi- 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.
How does the time taken to recharge a battery using charging system A compare with the time taken using charging system B?
[1 mark]
ANSWER
To compare the time the battery took to charge, we need to compare the power supplied by both the systems.
System A
System B
This shows us that the power supplied by B is twice greater than the power supplied by A. And therefore, the time taken by system A is double than the time taken by system B. This can be mathematically proven as
Electrical work done by both the systems is the same as the voltage across both is 230V.
So, time taken using system A is double the time of system B.
