Chapter 11

NCERT
Class 10
Science
Solutions
15. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to the electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

Question:

Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to the electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

Answer:

Let, Resistance for the first lamp = R1

Resistance for the second lamp = R2

P1 = 100W, P2 = 60W, V = 220V

From Formula :

R1 = V2/P1

R1 = (220 X 220) / 100

R1 = 484Ω

R2 = V2/P2

R2 = (220 X 220) / 60

R2 = 2420/3Ω

Connecting R1 and R2 in parallel series

R = (R1 X R2)/R1 + R2

R = (484 X (2420/3))/484 + (2420/3)

R = 2420/8

R = 605/2Ω

I = V/R

I = 220/(605/2)

I = 220 X 2/605

I = 0.72A

So, the current drawn from mains is 0.72 A.

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