Question

Two bulbs of 500 W and 300 W are manufactured to operate on 220 V line. The ratio of resistance of 500 W bulb to that of 300 W bulb is
(1) 3 : 5
(2) 5 : 3
(3) 9 : 25
(4) 25 : 9

Answer 1

option (A) 3:5

as power P=V^2/R

so R=V^2/P

v is constant so R is inversely proportional to P

so it will be 3:5

Answer 2

Correct Answer is option 1

3: 5

Explanation:

First bulb= v=220v

P=500w

P1= v²/R1

R1= V²/P1= 220x200/500 ohms

For second bulb :

v=220 v

P=300W

R2= v²/p=220x200/300

By taking ratios :

R1:R2= 220x200x 300: 500 x220x200  = 3: 5