Q. A screen receives $3\ watt$ of radiant flux of wavelength $6000\ \mathring{\mathrm{A}}$. One lumen is equivalent to $1.5 \times 10^{- 3}watt$ of monochromatic light of wavelength $5550\ \mathring{\mathrm{A}}$. If relative luminosity for $6000\ \mathring{\mathrm{A}}$ is 0.685 while that for $5550\ \mathring{\mathrm{A}}$ is 1.00, then the luminous flux of the source is
A) $4 \times 10^{3}lm$
B) $3 \times 10^{3}lm$
C) $2 \times 10^{3}lm$
D) $1.37 \times 10^{3}lm$
Explanation
(d) $\phi = \frac{3}{1.5 \times 10^{- 3}} \times 0.685 = 1.37 \times 10^{3}lumen$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.