Question

Two lamps, one rated 40 W at 220 V and the other 60 W at 220 V, are connected in parallel to the electric supply at 220 V.
(a) Draw a circuit diagram to show the connections.
(b) Calculate the current drawn from the electric supply.
​(c) Calculate the total energy consumed by the two lamps together when they operate for one hour.

Answer 1

(a)



(b) Using, $I=\frac{P}{V}$

Current drawn by 60 W lamp is, $I=\frac{220}{60}=3.67\mathrm{A}$

Current drawn by 40 W lamp is, $I=\frac{220}{40}=5.5\mathrm{A}$

So, the net current drawn by the combination is = 3.67 A + 5.5 A = 9.17 A

(c) Net power of the combination = 60 W + 40 W = 100 W

So, the energy consumed in 1 h = $E=P\times t$ = 100 × 1 × 60 × 60 J = 360000 J