Question

Three equal resistors connected in series across a source of emf together dissipate 5watt of power. If the same resistors are connected in parallel across the same source of emf, the power dissipated will be

Answer 1

When the three resistors are in series, effective resistance in the circuit = 3R.
Power dissipated in the series circuit = Pseries = V^2/(3R) = 5 W
⇒ V^2/(R) = 15W
When the three resistors are in parallel, effective resistance in the circuit = R/3.
Power dissipated in the parallel circuit = Pparallel = V^2/(R/3) = 3V^2/(R)
= 3 x 15 W = 45 W