Transformer equations-help!?

Question

i'm kind of stuck at the end of my homework. can someone help me out with this problem?

An ideal step-down transformer has a primary coil of 310 turns and a secondary coil of 21 turns. Its primary coil is plugged into an outlet with 220 V(AC), from which it draws an rms current of 0.13 A.

What is the voltage in the secondary coil?

Calculate the rms current in the secondary coil.

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

Answer 1

The ratio of the turns on primary and secondary is the same as the ratio of the pd in each.

The power input in watts is the same as the power output.

So 21/310 = v/220

so v = 220 x 21/310 = 14.9v

power in = 220 x 0.13 =28.6w

28.6 = 14.9 x I

so I = 28.6/14.9 = 1.92 A

Energy dissipated = I^2R