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The resistance of the filament of a lamp increases with the increase in temperature.  A lamp rated 100 W and 200 V is connected across 220 V power supply.  If the voltage drops by 10%, then the power of the lamp will be

a)

90 W

b)

81 W

c)

Between 90 and 100 W

d)

Between 81 and 90 W


Question ID - 151198 | Toppr Answer

The resistance of the filament of a lamp increases with the increase in temperature.  A lamp rated 100 W and 200 V is connected across 220 V power supply.  If the voltage drops by 10%, then the power of the lamp will be

a)

90 W

b)

81 W

c)

Between 90 and 100 W

d)

Between 81 and 90 W

1 Answer - 5876 Votes

3537

Answer Key : (d) -

(d)

Let the resistance of the lamp filament be   Then   When the voltage drops, expected power is

Here,  will be less than  because now the rise in temperature will be less.  Therefore,  is more than   But it will not be 90% of earlier value, because fall in temperature is small.  Hence, option (d) is correct.



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