Applied Electricity Paper 2 , Nov/Dec. 2014  
Questions:   1 2 3 4 5 6   Main
General Comments

Question 3

⦁ Explain briefly the basic principle of mutual induction in a transformer.
⦁ List two factors that determine the induced e.m.f. in a transformer winding.
⦁ Calculate the volts per turn for a transformer with primary turns of 1,100 when supplied with an alternating input of 110 V.




The expected answers were:
(a) An alternating flux set up by the circuit in the primary coil links the secondary
coil of the transformer thereby inducing an e.m.f. in the secondary coil. The
primary and secondary coils are electrically separated but magnetically coupled.
The e.m.f. induced can be expressed as
e = - m
where m = mutual inductance
= flux from the primary coil linking the secondary coil
t = time

(b) Any two factors listed below

Number of turns in the winding
Alternating current in the winding or coil
Alternating magnetic flux in the winding or coil
Winding or coil inductance
Alternating flux in the winding or coil
Change of current in the winding or coil
Change of flux in the winding or coil

(c) Volts per turn =
= 0.1 V/turn

The question was on Transformers. It was unpopular with the candidates. The
candidates that attempted this question did well only in parts (b) and (c). The
candidates’ performance was fair.


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