Question

Two bulbs have ratings 100 W, 220V and 60 W, 220 V. Which one has the greater resistance?

Answer 1

Explanation:

using the relation P=V2/R

since voltage across both the cells is same

so we conclude that resistance is inversely proportional to power

so the bulb with low power has greater resistance

Answer 2

you know as well, power is given as P = V²/R

where P represents power, V represents potential difference across bulb and R represents resistance of bulb.

case 1 : Power of bulb , P1 = 100W

potential difference, V1 = 220V

so, resistance of bulb , R1 = V1²/P1

= (220)²/100 = 484 Ω

case 2 : power of bulb, P2 = 60W

potential difference, V2 = 220V

so, resistance of bulb, R2 = V2²/P2

= (220)²/60 = 48400/60 = 4840/6 = 806.67 Ω

hence, it is clear that resistance of 2nd bulb is greater than that of first one.