Q. 1% of light of a source with luminous intensity $50\ candela$ is incident on a circular surface of radius $10\ cm$. The average illuminance of surface is
A) 100 $lux$
B) 200 $lux$
C) 300 $lux$
D) 400 $lux$
Explanation
(b) $\phi = 4\pi L = 200\ \pi\ lumen$
So $I = \frac{\phi}{100\ A} = \frac{200\ \pi}{100 \times \pi r^{2}} = \frac{2}{(0.1)^{2}} = 200\ lux$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.