Q. If separation between screen and source is increased by 2%, what would be the effect on the intensity
A) Increases by 4%
B) Increases by 2%
C) Decreases by 2%
D) Decreases by 4%
Explanation
(d) Intensity $\propto \frac{1}{r^{2}}$
$\frac{I_{2}}{I_{1}} = \left( \frac{r_{1}}{r_{2}} \right)^{2} = \left( \frac{r_{1}}{r_{1}(1 + 2\%)} \right)^{2}$
$I_{2} = I_{1}(1 + 2\%)^{- 2}$
Expanding by binomial theorem $\Rightarrow I_{2} = I_{1}(1 - 4\%)$
$\therefore$ Intensity decreases by 4%
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.