Question

a) An ideal step-down transformer has a primary coil of 400 turns and a secondary coil of 14 turns. Its primary coil is plugged into an outlet with 240 V(AC), from which it draws an rms current of 0.35 A. What is the voltage in the secondary coil?

b) Calculate the rms current in the secondary coil.

c) Assuming that the transformer secondary is driving a resistive load, calculate the average power dissipated in the resistor.

Answer 1

A) For a transformer with primary coil and secondry coil the relation between voltage across primary coil and voltage across secondy coil is given by

  

This voltage is the RMS voltage across the secondry coil as the voltage across primary coil was given as RMS.

B) In an ideal transformer the power in primary coil must be equal to the power in secondry coil. (this expresiion is true because our load is purely resistive). where are currents in primary and secondry coils respectively.

C) As already calculated P=240*0.35=84W