Chapter 11

NCERT
Class 10
Science
Solutions
2. An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source

Question:

An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it?

Answer:

Here, R1 = 100, R2 = 50, R3 = 500, and V = 220V

I1 = R1/V

I1 = 220/100

I2 = R2/V

I2 = 220/50

I3 = R3/V

I3 = 220/500

⇒ Total current = I1 + I2 + I3

I = 220/100 + 220/50 + 220/500

I = 220 (1/100 + 1/50 + 1/500)

I = 220 ((5 + 10 + 1)/500)

I = 220 (16/500)

I = 220 X 0.032 A

I = 7.04 A

R if iron = V/I

R = 220/7.04

R = 31.25 Ω

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