Current Electricity Question 24
Question 24 - 2024 (31 Jan Shift 2)
By what percentage will the illumination of the lamp decrease if the current drops by $20 %$ ?
(1) $46 %$
(2) $26 %$
(3) $36 %$
(4) $56 %$
Show Answer
Answer: (3)
Solution:
$\mathrm{P}=\mathrm{i}^{2} \mathrm{R}$
$\mathrm{P}{\text {int }}=\mathrm{I}{\text {int }}^{2} R$
$\mathrm{P}{\text {final }}=\left(0.8 \mathrm{I}{\text {int }}\right)^{2} \mathrm{R}$
$%$ change in power $=$
$\frac{\mathrm{P}{\text {final }}-P{\text {int }}}{\mathrm{P}_{\text {int }}} \times 100=(0.64-1) \times 100=-36 %$
