By what percentage will the illumination of the lamp decrease if the current drops by 20% ?

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Solution

Q.
By what percentage will the illumination of the lamp decrease if the current drops by 20% [2024]

1 46%

2 26%

3 36%

4 56%

Ans.
(3)

$P_{i n i t i a l} = {I^{2}}_{i n i t i a l} R$

$P_{f i n a l} = {(0.8 I_{i n i t i a l})}^{2} R$

% change in power

$\frac{P_{f i n a l} - P_{i n i t i a l}}{P_{i n i t i a l}} \times 100 = (0.64 - 1) \times 100 = - 36 %$

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