Question

The luminous efficiency of a lamp is $8.8$ lumen/watt and its luminous intensity is $700Cd$. The power of the lamp will be

• A. ${10}^1$ $W$
• B. ${10}^2$ $W$
• C. ${10}^3$ $W$
• D. ${10}^4$ $W$

Answer 1

Answer: (C)

${10}^3$ $W$

$Luminousflux=Luminousintensity\ast solidangle$

Total solid angle = 4 $\pi$

So, Luminous flux = 700 x 4 $\pi$

Luminous flux = Luminous efficiency x power

=> 700 x 4 $\pi$ = 8.8 x power

=> Power of lamp = 1000 W

Answer. C) 10${}^3$ W