Question

In a cinema hall the distance between the projector and the screen is increased by 2 %. Now the intensity of illumination of the screen

• A. decreases by 4%
• B. increases by 2%
• C. decreases by 2%
• D. increases by 4%

Answer 1

Answer: (A)

decreases by 4%

Answer 2

$\frac{I_2}{I_1}=\frac{d_1^2}{1.02\,d^2_1}=0.96 \left(\because 1 \propto \frac{1}{d^2}\right) i.e.,I_2 =0.96 \,I_1$ Decrease =$I_1 - I_2 = 1 - 0 96 \,I_1 = 0-04 i.e. 4$