A step-down transformer has a primary coil of 1200 turns and a secondary coil of 150 turns. The primary coil is connected to an alternating current (a.c.) mains supply with a root-mean-square (r.m.s.) voltage of 240 V. The secondary coil is connected to a heating element of resistance 15 Ω.
Assuming the transformer is 100% efficient, what is the peak power dissipated in the heating element?
30 W30\text{ W}30 W
60 W60\text{ W}60 W
120 W120\text{ W}120 W
240 W240\text{ W}240 W