NEET-XII-Physics
22: Photometry
- #2A photographic plate records sufficiently intense lines when it is exposed for 12 s to a source of 10 W. How long should it be exposed to a 12 W source radiating the light of same colour to get equally intense lines?Ans : Let t be the time for which the photograph is exposed.
To record the sufficiently intense lines, energy should be same.
Energy = radiant flux × time
= 10 W×12 s
= 12 W×t
`` \Rightarrow t=\frac{10\,\mathrm{\,W\,}\times 12\,\mathrm{\,s\,}}{12\,\mathrm{\,W\,}}``
`` =10\,\mathrm{\,s\,}``
Therefore, the photographic plate should be exposed for 10 s to get equally intense lines.
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