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 5W, 10W or 15W. What should be the resistances of the filaments?

Question

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 5W, 10W or 15W. What should be the resistances of the filaments?

Philoid · Accepted Answer

and

Given, Voltage of the battery,

Power operated P=5W, 10W or 15W

We know,

Now,

The parallel combination of resistances is always less than individual resistances. Therefore, has to be parallel combination while and are the resistances.