Question

Two electric bulbs marked 100 W 220V and 200W 200V have tungsten filament of same length. Which of the two bulbs will have thicker filament ?

Answer 1

We know, P = VI

For 100 W, 220 V rating bulb, I = P/V = 100/220 = 0.4545 A

So, maximum resistance offered is, R = V/I = 220/0.4545 = 484 Ω

For 220 W, 200 V rating bulb, I = 220/200 = 1.1 A

So, maximum resistance offered is, R = V/I = 200/1.1 = 181.82 Ω

Now, resistance is inversely proportional to thickness. Since, 220 W bulb has low resistance, its filament’s thickness will be more.