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Question:

Two equal resistances when connected in series to a battery, consume electric power of 60W. If these resistances are now connected in parallel combination to the same battery, the electric power consumed will be?

240W

60W

30W

120W

Solution:

The correct option is A 240W

In series condition, equivalent resistance is 2R
Power consumed P = V²/2R = 60W
In parallel condition, equivalent resistance is R/2
Power consumed P' = V²/(R/2) = 2V²/R = 4(V²/2R) = 4 * 60W = 240W