Two lamps, one rated 40 W at 220 V and the other 100 W at 220 V, are connected in parallel to the electric supply at 220V.
(a) Draw a circuit diagram to show the connections.
(b) Calculate the current drawn from the electric supply.
(c) Calculate the total energy consumed by the two lamps together when they operate for one hour.

Options

A. 25 W
B. 14 W
C. 60 W
D. 100 W

Answer

B

Explanation

Resistance of bulb 1
`R_(1)=(V^(2))/(P)=((220)^(2))/(100)`
`R_(1)=484Omega`
Resistance of bulb 2
`R_(2)=((220V)^(2))/(60W)=(4840)/(6)=806.6Omega`
`R_(eq)=R_(1)+R_(2)=(220)^(2)((1)/(100)+(1)/(60))`
Current flowing, `I=(220V)/(R_(eq))=(220)/((220)^(2))((100xx60)/(160))`
`I=(1)/(220)((75)/(2))=(15)/(88)A`
Power consumed by 100 W bulb = `I^(2)R_(1)`
`=((15)/(88))^(2)xx((220)^(2))/(100)=(225)/(16)=14W`