Q. Five $lumen/watt$ is the luminous efficiency of a lamp and its luminous intensity is $35\ candela$. The power of the lamp is
A) $80\ W$
B) $176\ W$
C) $88\ W$
D) $36\ W$
Explanation
(c) Efficiency of light source
$\eta = \frac{\phi}{P}\ \ \ $…(i) and $L = \frac{\phi}{4\pi}$ …(ii)
From equation (i) and (ii)
$\Rightarrow P = \frac{4\pi L}{\eta} = \frac{4\pi \times 35}{5} \approx 88\ W$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.