If two bulbs of wattage 25 and 100 respectively each rated at 220 volt are connected in series with the supply of 440 volt , then which bulbs will fuse

Options

A. 100 W bulb
B. 25 W bulb
C. None of these
D. Both of these

Answer

B

Explanation

Resistance of 25W bulb `R_(1)=(V^(2))/(P)=((220)^(2))/(25)=1936Omega`
Resistance of 100W bulb
`R_(1)=(V^(2))/(P)=((220)^(2))/(100)=484Omega`
Series resistance `=R_(1)+R_(2)`
`=1936+484=2420Omega`
Current through series combination will be
`I=(440)/(2420)=(2)/(11)A`
`V_(1)=R_(2)xx I=484 xx (2)/(11)=88V`
Thus the bulb of 25W will be fused because it can tolerate only 220V while the voltage across it is 352V.