Question

If voltage across a lamp increases by 2% then percentage change in power is

Answer 1

If the voltage across a lamp increases by 2% then the percentage change in power is 4%.

Explanation:

Let the initial voltage across the lamp be “V1” and the initial power be “P1”.

 

In both cases, the resistance remains constant, so the initial power of the lamp will be given as,

P1 = $\frac{V1^2}{R}$ …… (i)

Now,

The voltage across the lamp increases by 2% i.e.,

The final voltage, V2 = V1 + 0.02V1 = 1.02V1

Then, the final power across the lamp will be,  

P2 = $\frac{V2^2}{R} = \frac{(1.02V1)^2}{R} = \frac{1.04 V1^2}{R}$ = 1.04 P1 …… [substituting from (i)] ….. (ii)  

Thus,

The percentage change in power will be,

= $\frac{P2 - P1}{P1} * 100$

= $\frac{1.04P1 - P1}{P1}$ * 100

= 4%

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Answer 2

Answer:4%

Explanation: