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

Answer 1

The various resistances of the bulbs =$\frac{v^2}{p}$

Resistances are

$\frac{(15{)}^2}{5},\frac{(15{)}^2}{10},\frac{(15{)}^2}{15}=45,22.5,15$

Since two resistances when used in parallel have resistances less than both. The resistances are 45 & 22.5