A transformer is rated 240V. If the primary coil is 4000 turns and the secondary voltage 12V; determine the number of turns in the secondary coil.

A. 200
B. 100
C. 250
D. 150

Correct Answer:

Option A – 200

Explanation

in a transformer, ES/EP = Ns/Np
where Es = e.m.f (voltage) of the secondary
Ep = e.m.f(voltage)of the primary
Ns = no. of turns in the secondary
Np = no. of turns in the primary.
since Es = Vs; and Ep= Vp.
Vs/ Vp= Ns/Np
∴12/240= Ns/4000
Ns =(12×4000)/240
=200