A) \[\frac{1}{200}\]
B) \[\frac{1}{800}\]
C) \[\frac{1}{6400}\]
D) \[\frac{1}{3200}\]
Correct Answer: B
Solution :
The time of exposure that is duration of time for which film is to be exposed depends on the condition of light. The time of exposure for good quality prints depends on both\[f-\]number and E-number. \[T\times {{\left( \frac{1}{f-number} \right)}^{2}}\left( \frac{1}{E-number} \right)\] \[Where\,f-number\times \frac{1}{focal\,length}\] \[\Rightarrow \] \[\frac{{{T}_{1}}}{{{T}_{2}}}=\frac{f_{1}^{2}}{f_{2}^{2}}\] Given, \[{{f}_{1}}=5f,{{f}_{2}}=2.5f,{{T}_{1}}=\frac{1}{200}s\] \[{{T}_{2}}=\frac{{{T}_{1}}f_{2}^{2}}{{{f}_{1}}}=\frac{1}{200}\times \frac{{{(2.5)}^{2}}}{{{(5)}^{2}}}\] \[{{T}_{2}}=\frac{1}{800}s\].
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