Question 4
(a) Define the term electromagnetic induction.
(b) List two factors that influence the magnitude of induced e.m.f. in a coil.
(c) The current in a coil changes from 4 A to 1 A in 0.4 seconds. If the induced e.m.f. is 50 V, calculate the:
(i) inductance of the coil;
(ii) energy stored in the coil.
Observation
The expected responses were:
- Electromagnetic induction may be defined as the induction of voltage in a coil, due to the change with time, of the magnetic flux linking with the coil.
- Magnitude of emf induced in the coil depends on:
- time rate of change of current through the coil;
- inductance of the coil;
- Number of turns of coil;
- time rate of change of flux linkage;
- flux density;
- length of coil;
- velocity of the conductor;
(ii) There are three possible answers to this question, as posed:
Question 4 required candidates to respond to recall about electromagnetic induction in the first task and apply some facts in solving the problem given in the second task. While majority of the candidates were said to have responded well the question in general, it was however reported that the major difficulty many candidates had with this question was with the computation of energy stored in the magnetic field of the inductor.