Three 40, 60 and 100 W lamps are first connected in series and then in parallel. Supply voltage 220 V.

Three 40, 60 and 100 W lamps are first connected in series and then in parallel. Supply voltage 220 V. Determine lamp currents and total current for each connection.

When connected in series, the total power is equal to the sum of the consumed powers:
P = 40 + 60 + 180 = 280 W
And the current flowing through the lamps will be the same and equal to the total current:
I = P / U = 280/220 = 1.27 A.
When connected in parallel, the currents through each of the lamps are equal:
40/220 = 0.18 A
60/220 = 0.27 A
100/220 = 0.45 A.
The total current is equal to the sum of these currents:
0.18 + 0.27 + 0.45 = 0.9 A.