An electric car is propelled by a direct current (d.c.) motor, and this motor is supplied by a direct current power supply. Fig. 6.1 shows the motor circuit. Point P is located in the circuit between the motor and the positive terminal of the power supply. In the circuit diagram, point P appears to the left of the motor. Over a time interval of 120 s, the current in the circuit at point P is 41 A.
(a)[1]
Describe how a direct current differs from an alternating current (a.c.).
(b(i))[2]
Calculate the charge that passes through point P in the time of 120 s.
(b(ii))[2]
The current in the circuit is produced by the movement of electrons. Each electron has a charge magnitude of $1.6 \times 10^{-19}\,\text{C}$. State the direction which the electrons move past point P and determine the number of electrons that pass point P in 1.0 s.
(c(i))[2]
The e.m.f. (electromotive force) of each cell is 3.7 V. Define the term ‘electromotive force’.
(c(ii))[2]
Each battery consists of 92 cells in series. Calculate the e.m.f. of one battery.
(c(iii))[1]
The power supply is assembled by connecting 85 of these batteries in parallel. State the e.m.f. of the power supply.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “A d.c. current; travels in one direction; does not keep reversing direction; polarity/direction remains unchanged” …