Q151 / 170 · Manipal (MET) 2020 · Physics
A convex lens of focal length 0.12 m produces an image, which is three times as long as the object. The distance between the object and the lens for a real image
- Correct answerA$0.16 m$
- B$-0.16 m$
- C$1.6 m$
- D$-1.6 \mathrm{~m}$
Solution
Magnification produced by the lens
$B=\frac{\mu_0 N i}{2 \pi r}$
$m=\frac{v}{u}=-3 \Rightarrow v=-3 u$
Applying lens of formula, we have
$\begin{array}{ll} & \frac{1}{v}-\frac{1}{u}=\frac{1}{f} \\ \Rightarrow & \frac{1}{-3 u}-\frac{1}{u}=\frac{1}{0.12} \\ \text { or } & \frac{-1-3}{3 u}=\frac{100}{12}=\frac{25}{3} \\ \text { or } & -\frac{4}{3 u}=\frac{25}{3}\end{array}$
or $\quad u=-\frac{4}{25} m=0.16 \mathrm{~m}$
Hence, the correct answer is option: 'A'.