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Correct exposure for a photographic print is 10 s at a distance of one metre from a point source of 20 cd. For an equal fogging of the print placed at a distance of 2 m from a 16 cd source, the necessary time for exposure is |
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Answer» 100 s `I_(2)xxt_(2)=I_(1)xxt_(1)` or`L_(2)/r_(2)^(2)xxt_(2)=L_(1)/r_(1)^(2)xxt_(1)` or`16/4xxt_(2)=20/1xx10` `therefore``t_(2)=50 s` |
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