Question

A lamp hanging 4 m above the table is lowered by 1 m. The illumination on the table

• A. decreases by 77.7%
• B. increases by 77.7%
• C. decreases by 25%
• D. increases by 25%

Answer 1

Answer: (B)

increases by 77.7%

Answer 2

$\frac{I_2}{I_1}=\frac{d^2_1}{d^2_2}i.e., \frac{I_2 -I_1}{I_1}=\frac{4^2 -3^2}{3^2}=\frac{7}{9}=0.777$
77.7% increase.