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

Explanation

The various resistances of the bulbs = ` v^2/p`
` Resistance are `
` ((15)^2/5), (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 & 22.5 .