The voltage across a bulb is decreased by 2%. Assuming that the resistance of

Discussion Forum : Current Electricity

Question -

The voltage across a bulb is decreased by $2 % .$ Assuming that the resistance of the filament remains unchanged the power of the bulb will

Options:

A . decrease by

2 %

B . increase by

2 %

C . decrease by

4 %

D . increase by

4 %

Answer: Option C
:
C

Power $P = \frac{v^{2}}{R}$
Therefore $△ P = \frac{2 V △ V}{R}$
Hence $\frac{△ P}{P} = \frac{2 △ V}{V}$
Now $\frac{△ V}{V} = - 2 %$
Therefore $\frac{△ P}{P} = - 2 \times 2 = - 4 %$ i.e. the power decreases by $4 %$

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