Question

The light bulb and rheostat are connected in series and powered from a constant current source.
The resistance of the rheostat and the voltage at the terminals of the light bulb are known: 10  and 40 V.
The external circuit consumes 120 W of power. Find the current in the circuit.

Answer 1

$I = \frac{P}{V} = \frac{120}{40}=3A$