Q. If luminous efficiency of a lamp is 2 lumen/watt and its luminous intensity is 42 candela, then power of the lamp is
A) $62\ W$
B) $76\ W$
C) $1.38\ W$
D) $264\ W$
Explanation
(d) Luminous flux $= 4\pi\ L = 4 \times 3.14 \times 42 = 528\ Lumen$
Power of lamp $= \frac{Luminous\ flux}{Luminous\ efficiency} = \frac{528}{2} = 264\ W$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.