Q157 / 160 · WBJEE 2011 · Physics

A convex lens of focal length \(30 \mathrm{~cm}\) produces 5 times magnified real image of an object. What is the object distance ?

  • Correct answer
    A
    \(36 \mathrm{~cm}\)
  • B
    \(25 \mathrm{~cm}\)
  • C
    \(30 \mathrm{~cm}\)
  • D
    \(150 \mathrm{~cm}\)

Solution

Hints: \(\frac{1}{5 \mathrm{u}}-\left(\frac{1}{-\mathrm{u}}\right)=\frac{1}{30}\) \(\begin{aligned} & \frac{1}{5 \mathrm{u}}+\frac{1}{\mathrm{u}}=\frac{1}{30}, \frac{5+1}{5 \mathrm{u}}=\frac{1}{30} \\ & \mathrm{u}=36 \mathrm{~cm} . \end{aligned}\)

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

Relevant Questions