If two electric bulbs have 40 W and 60 W rating at V 220 , then the ratio of their resistances will be

Options

A. 10 ohm
B. 20 ohm
C. 30 ohm
D. 40 ohm

Answer

C

Explanation

`i=90/30 = 3A, R_(b) = (30)^(2)/90 =(30 xx 30)/90 = 10 Omega`
`i=120/(10+ R) rArr 3 = 120/(10+ R) rArr R = 30 Omega`