Electric power of a circuit is defined as the rate at which the work is done by the source of emf in maintaining the current in electric circuit. Electric power is given as
where V is the potential difference, I is the current, and R is the resistance.
(i) When two bulbs rated (P1, V) and (P2,V) are connected in series:
The current is the same through each bulb. If R1 and R2 are resistances of two bulbs, then the effective resistance of the circuit is
R = R1 + R2
Using the relation
we have
Given: V1 = V2 = V. Therefore,
Thus, the effective power when two bulbs are connected in series is
(ii) When two bulbs rated (P1, V) and (P2,V) are connected in parallel
Using the relation
we get
Given: V1 = V2 = V. Therefore,
Thus, the effective power when two bulbs are connected in parallel is
P = P1 + P2.
