First slide

Electrical power

Question

If resistance of the filament increases with temperature, what will be power dissipated in a $220 V - 100 W$ lamp when connected to 110 V power supply?

Moderate

A

25 W
B

< 25 W
C

> 25 W
D

None of these

Solution

If resistance does not vary with temperature, power consumed $= {(\frac{V_{A}}{V_{R}})}^{2} \times P_{R} = {(\frac{110}{220})}^{2} \times 100 = 25 W .$ But in second cases resistance decreases, so consumed power will be more than 25 W.

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