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A bulb is made using two filaments. A switch selects whether the filaments are used individually or in parallel. When used with a 15 V battery, the bulb can be operated at 5 W, 10 W or 15 W. What should be the resistances of the filaments?

A bulb is made using two filaments. A switch selects whether the filaments are used individually or in parallel. When used with a 15 V battery, the bulb can be operated at 5 W, 10 W or 15 W. What should be the resistances of the filaments?

Grade:11

1 Answers

Aditi Chauhan
askIITians Faculty 396 Points
9 years ago
Sol. The various resistances of the bulbs = V^2/P Resistances are (15)^2/10, (15)^2/10, (15)^2/15 = 45, 22.5, 15. Since two resistances when used in parallel have resistances less than both. The resistances are 45 and 22.5.

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