1. Tardigrade
  2. Question
  3. Physics
  4. An object placed in front of a concave mirror at a distance of x cm from the pole gives a 3 times magnified real image. If it is moved to a distance of (x+5) cm, the magnification of the image becomes 2. The focal length of the mirror is

Question Error Report

Thank you for reporting, we will resolve it shortly

Back to Question

Q. An object placed in front of a concave mirror at a distance of $x \,cm$ from the pole gives a $3$ times magnified real image. If it is moved to a distance of $(x+5)\, cm$, the magnification of the image becomes $2$. The focal length of the mirror is

WBJEEWBJEE 2012Ray Optics and Optical Instruments

Solution:

Given $v_{1}=3 x$ and $v_{2}=2(x+5)$
So here, Ist case
$\frac{1}{-x}+\frac{1}{-3 x}=\frac{1}{f}$ ...(i)
$\frac{1}{-(x+5)}+\frac{1}{-2(x+5)}=\frac{1}{f}$ ...(ii)
On solving Eqs. (i) and (ii) we get $f=30\, cm$