# Transformer changes 216 V across the primary to 12 V across the secondary. If the secondary coil has 10 turns, how many turns does the primary coil have?

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The voltage induced in the secondary winding of a transformer is a function of the voltage applied to the primary winding and the ratio of number of turns in the primary winding to the secondary winding. Mathematically, this relationship is given as:

Vs/Vp = Ns/Np

Where, Vs and VP are voltages in secondary and primary windings and the Ns and Np are the number of turns in secondary and primary windings, respectively.

Here, Vs= 12 V, Vp= 216 V, Ns= 10 .

Thus, Np = Ns x Vp/Vs = 10 x 216/12 = 180 turns.

Thus the primary coil of the transformer has 180 turns. Each turn of the winding has the same induced emf in both the primary as well as the secondary winding turn. This induced emf is equal to 216/180 = 12/10 = 1.2 V.

Hope this helps.