Question

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%

Answer 1

Answer: (D)

Decreases by 4%

Answer 2

$I \propto \frac{1}{r^{2}}$ ⇒ $\frac{\Delta I}{I} = - 2\frac{\Delta r}{r}$=$- 2 \times 2 = - 4\%$

Hence intensity is decreased by 4%.