Q. In a movie hall, the distance between the projector and the screen is increased by 1% illuminates on the screen is
A) Increased by 1%
B) Decreased by 1%
C) Increased by 2%
D) Decreased by 2%
Explanation
(d) $I = \frac{L}{r^{2}}$
$\Rightarrow \frac{dI}{I} = - \frac{2dr}{r}\ \ \ \ \ \ \ \ \ \ \ \lbrack\because L = constant\rbrack$
$\Rightarrow \frac{dI}{I} \times 100 = - \frac{2 \times dr}{r} \times 100 = - 2 \times 1 = - 2\%$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.