A) 90 W
B) 81 W
C) between 90 and 100W
D) between 81 and 90W
Correct Answer: D
Solution :
Let the resistance of the lamp filament be R. Then,\[100={{(200)}^{2}}/R\]. When the voltage drops, expected power is\[P={{(220\times 0.9)}^{2}}/R'\]Here, R' will be less than R, because now the rise in temperature will be less. Therefore, P is more than\[{{(220\times 0.9)}^{2}}/R=81\text{ }W\]. But it will not be 90% of earlier value, because fall in temperature is small. Hence, option is correct.
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