By what percentage will the illumination of the lamp decrease if the current drops by $20 \%$ ?
JEE MAIN 2024, Diffcult
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$P=i^2 R$
$P_{\text {int }}=I^2{ }_{\text {int }} R$
$P_{\text {final }}=\left(0.8 I_{\text {int }}\right)^2 R$
$\% \text { change in power }=$
$\frac{P_{\text {final }}-P_{\text {int }}}{P_{\text {int }}} \times 100=(0.64-1) \times 100=-36 \%$
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