Q144 / 180 · AIIMS 2007 · Physics

The camera lens has an aperture of \(f\) and the exposure time is \((1 / 60) \mathrm{s}\). What will be the new exposure time if the aperture become \(1.4 f\) ?

  • A
    \(\frac{1}{42}\)
  • B
    \(\frac{1}{56}\)
  • C
    \(\frac{1}{72}\)
  • Correct answer
    D
    \(\frac{1}{31}\)

Solution

Time of exposure \(\propto f^2\) \(\begin{aligned} & \frac{1}{60} \times \frac{1}{1}=\frac{t}{1.4^2} \Rightarrow t=0.03266 \mathrm{~s} \\ & t=\frac{1}{31} \mathrm{~s} . \end{aligned}\)

Hence, the correct answer is option: 'D'.

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