Question

1.
Lamp A is rated at 100 watt, 220 volt and lamp B rated a
150 watt 220 volt are connected in series across 220 volt supply.
Calculate (i) the respective voltage across each lamp, (ii) power
consumption. What will be the total power if the two lamps are
connected in parallel across 220 volt supply?​

Answer 1

When lamps are connected in series

P1 = 35.28 W ; P2 = 23.55 W

When lamps are connected in parallel then the total power will be

P = 249.85 W

Explanation:

i) First we will find the rated resistances, then current and power.

R1 = V^2 /p1 = (220)^2/100 = 484 ohm

R2 = V^2 /p2 = (220)^2/150 = 323 ohm

Now,

I = V / (R1+ R2)

I = 220 / (484+323 )

I = 0.27 A

Now,

PR1 = (0.27)^2 * (484) = 35.28 W

PR2 = (0.27)^2 * (323) = 23.55 W

ii) When both lamps are connected in parallel then:

Equivalent resistance =  193.71 ohm

Total power = (220)^2/193.71

Total Power = 249.845 W