Q. The maximum illumination on a screen at a distance of $2\ m$ from a lamp is $25\ lux$. The value of total luminous flux emitted by the lamp is
A) $1256\ lumen$
B) $1600\ lumen$
C) $100\ candela$
D) $400\ lumen$
Explanation
(a) $I = \frac{L}{r^{2}} \Rightarrow L = I.r^{2} = 25 \times 2^{2} = 100$
Now $\phi = 4\pi L = 4 \times 3.14 \times 100 = 1256\ lumen$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.