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Time of exposure for a photographic print is 10 seconds, when a lamp of 50 cd is placed at 1 m from it. Then another lamp of luminous intensity I is used, and is kept at 2 m from it. If the time of exposure now is 20 s, the value of I (in cd) is

Option: 1

25


Option: 2

100


Option: 3

200


Option: 4

20


Answers (1)

\mathrm{v=\frac{c}{\lambda}=\frac{3 \times 10^{8}}{1}=3 \times 10^{8} \mathrm{~Hz}}
\mathrm{v^{\prime}=\frac{c}{\lambda^{\prime}}=\frac{3 \times 10^{8}}{10}=3 \times 10^{7} \mathrm{~Hz}}

Posted by

Ramraj Saini

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