How many turns should the secondary winding of a step-down transformer have, the primary winding

How many turns should the secondary winding of a step-down transformer have, the primary winding of which has 1200 turns, if the voltage is to be reduced from 120 V to 4 V?

Data: N1 (the number of turns that the primary winding of the transformer has) = 1200 turns; U1 (voltage on the primary winding) = 120 V; U2 (voltage that should be on the secondary winding) = 4 V.

The number of turns on the secondary winding of the transformer is determined from the formulas for calculating the transformation ratio: k = N1 / N2 = U1 / U2, whence N2 = U2 * N1 / N2.

Let’s calculate: N2 = 4 * 1200/120 = 40 turns.

Answer: The secondary winding of the step-down transformer must have 40 turns.