Question

An object of height 12 cm is kept 1.2 m far from a convex lens of focal length 80 cm. Find the height of the image.

Answer 1

Explanation:

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Answer 2

The image height is -24 cm when object height is 12 cm kept 1.2 m far from convex lens of focal length 80 cm.

Explanation:

Height of the object = 12 cm

Focal length = 80 cm

Distance of object from the lens,that is,u =  1.2 m = 120 cm = - 120 cm

Lens maker formula, $\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$

For the convex lens

$\begin{array}{l}{\frac{1}{f}=\frac{1}{v}-\frac{1}{u}} \\ {\frac{1}{80}=\frac{1}{v}-\frac{1}{-120}} \\ {\frac{1}{80}=\frac{1}{v}+\frac{1}{120}} \\ {\frac{1}{80}-\frac{1}{120}=\frac{1}{v}}\end{array}$

$\frac{3-2}{240}=\frac{1}{v}$

v=240 cm

From magnification, $m=\frac{v}{u}$

$m=\frac{v}{u}=\frac{\text { height of the image}}{\text {height of the object}}=\frac{240}{-120}$

Height of the image= -24 cm