A focal length of a thin biconvex lens is 20 cm. When an object is moved from a distance of 25cm in front of it to 50cm, the magnification of its image changes from $m_{25}to\ m_{50}.$The ration $\frac{m_{25}}{m_{50}}$ is

Question

Dr. Abubacker · Accepted Answer

(a) $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$
$Or\ \frac{u}{v} - 1 = \frac{u}{f}$
$Or\ \frac{u}{v} = \left( \frac{u + f}{f} \right)$
$m = \frac{v}{u} = \left( \frac{f}{u + f} \right)$
$\frac{m_{25}}{m_{50}} = \frac{\left( \frac{20}{- 25\  + \ 20} \right)}{\left( \frac{20}{- 50\  + \ 20} \right)} = 6$

Q. A focal length of a thin biconvex lens is 20 cm. When an object is moved from a distance of 25cm in front of it to 50cm, the magnification of its image changes from $m_{25}to\ m_{50}.$The ration $\frac{m_{25}}{m_{50}}$ is

Explanation

Reviewed by Dr. Abubacker

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