JEE Advanced 2010 Physics question
Incandescent bulbs are designed by keeping in mind that the resistance of their filament increases with the increase in temperature. If at room temperature, 100 W, 60 W and 40 W bulbs have filament resistances , and , respectively, the relation between these resistances is
Answer: (D)
Solution
All the bulbs are rated for the same supply voltage V, and the rated power is , so at the working temperature : the 100 W bulb has the smallest and the 40 W bulb the largest hot resistance. The filaments are of the same material and the room-temperature resistance is
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