Question

The focal length of a concave lens is 20cm .At what distance an object must be placed infront of it to get its image at a distance of 12cm from the lens?​

Answer 1

Answer:

Focal length   f=−20 cm

Object distance  u=−50 cm

Using   v1−u1=f1

Or    v1−(−50)1=−201

We get   v=−14.3 cm

Since, v is negative. So image formed is virtual.

Hence, virtual image is formed at a distance of 14.3 cm in front of the lens.

Explanation:

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