a 230v/30v with 50Hz transformer that has a primary current of 0.6A which supply's number of 30v and 30 watts halogen light bulb. what is the efficiency?

Pi = Ep * Ip = 230 * 0.6 = 138 Watts = Power in.

Is = Ep/Vs * Ip = 230/30 * 0.6 = 4.6A. = Current in secondary or output.
Po = Vs * Is = 30 * 4.6 = 138 Watts. = Power out.
Assuming the given information is correct, Po = Pi = 138 Watts; but 4.6 light bulbs are required to consume 138 Watts. So we'll have to use 4 light
bulbs which consumes only 120 Watts(Po).

Efficiency = (Po/Pi) * 100% = (120/138) * 100% =