Question

A step-down transformer has a turn's ratio of 1:20, and its primary is connected across the terminal of a standard 120-V wall socket. A 300-Ohm resistor is connected across the secondary of this transformer. What power P is dissipated in the resistor?

Answer 1

The tension in the secondary is

$V_S=V_P\frac{N_S}{N_P}=20V_P=2400V$

Thus

$P=\frac{V_S^2}{R}=19200W$

I'm not sure if I correctly understood the turns ratio: if I w as wronf andthe secondary has 1/20 of the primary turns then

$V_S=V_P\frac{N_S}{N_P}=\frac{V_P}{20}=6V$

and power is

$P=\frac{V_S^2}{R}=0.12W$