Question

A concave lens of focal length 20 cm is placed at a distance of 20 cm from a 2 cm object which is placed perpendicularly to the principal axis. Find the size of the image formed.

Answer 1

Answer on Question #75513-Physics-Optics

A concave lens of focal length $20~\mathrm{cm}$ is placed at a distance of $20~\mathrm{cm}$ from a $2~\mathrm{cm}$ object which is placed perpendicularly to the principal axis. Find the size of the image formed.

Solution

$$\frac {1}{f} = \frac {1}{v} - \frac {1}{u}$$ $$\frac {1}{- 2 0} = \frac {1}{v} - \frac {1}{- 2 0}$$ $$\frac {1}{v} = \frac {- 1}{1 0}$$

Image distance

$$v = - 1 0 \mathrm{~cm}.$$

Magnification,

$$M = \frac {v}{u} = \frac {- 1 0}{- 2 0} = 0. 5$$ $$h = 0. 5 (2) = 1 \mathrm{~cm}.$$

Answer: 1 cm.

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