A 30 V , 90 W lamp is to be operated on a 120 V DC line. For proper glow, a resistor of Ω should be connected in series with the lamp.

Question

A 30 V , 90 W lamp is to be operated on a 120 V DC line. For proper glow, a resistor of Ω should be connected in series with the lamp., 40, 10, 20, 30

MARKS App · Accepted Answer

Resistance of the lamp, R 0 = V 2 P = 30 2 90 = 10 Ω Current in the lamp, i = 30 10 = 3 A When lamp is operated on a 120 V , then resistance, R ′ = V ′ i = 120 3 = 40 Ω Thus, for proper glow, the resistance required to the put in series will be R = R ′ - R 0 = 40 - 10 = 30 Ω

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