Question

The luminous efficiency of a lamp is $5$ lm $W^{-1}$ and its luminous intensity is $30$ candela. The power of the lamp will be

• A. $6\pi$ $W$
• B. $12\pi$ $W$
• C. $24\pi$ $W$
• D. $48\pi$ $W$

Answer 1

The correct option is C $24\pi$ $W$

$Luminousflux=luminousintensity\ast 4\pi$

$⟶$ F = $30\ast 4\pi lm$

Luminous efficiency = $5lm/W$

Power = $F/Power$

= $30\ast 4\pi /5=24\pi$

Answer. C) $24\pi W$