NEET-XII-Physics
22: Photometry
- #8A source emits 31.4 W of radiant flux distributed uniformly in all directions. The luminous efficiency is 60 lumen watt-1. What is the luminous intensity of the source?Ans : Given that,
Radiant flux = 31.4 W
Since the radiant flux is distributed uniformly in all directions, the solid angle will be 4`` \,\mathrm{\,\pi \,}``
Luminous efficiency = 60 lumen/W
So, luminous flux = luminous efficiency `` \times `` radiant flux
= 60 × 31.4 lumen
Luminous intensity = `` \frac{\,\mathrm{\,Luminous\,}\,\mathrm{\,Flux\,}}{\,\mathrm{\,Solid\,}\,\mathrm{\,angle\,}}=\frac{\,\mathrm{\,Luminous\,}\,\mathrm{\,Flux\,}}{4\,\mathrm{\,\pi \,}}``
`` =\frac{60\times (31.4)}{4\,\mathrm{\,\pi \,}}``
`` =150\,\mathrm{\,candela\,}``
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