Question

15. Two bulbs have the following ratings:
1. 40 W, 220 V
2. 20 W, 100 V
The ratio of their resistance is
(a) 1:2
(b) 2:1
(c) 1:1
(d) 1:3​

Answer 1

Answer:

40w,220v=1:1 and 20w,100v=1:2

Explanation:

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Answer 2

Answer: 2:1

Explanation:

Let the resistance of the first bulb be R1 and that of the second bulb be R2, power of the first bulb be P1 and that of the second bulb be P2 and the voltage of the first bulb be V1 and that of the second bulb be V2.

R1= V1²/P1

= 220²/40

R1 =1210

R2 = V2²/P2

=100²/20

R2= 500

R1/R2= 1210/500

2.42/1 ≈ 2:1 (approx)