Question

a convex lens has a focal length of 20cm. calculate at what distance from the lens should be an object placed so that it forms an image at a distance of 40cm​

Answer 1

Answer:

the answer is 40 cm infront of the lens.

please mark this answer as the brainliest..

Answer 2

The answer is 40 cm.

Given:

A convex lens with a focal length of 20 cm

The image distance is 40 cm

To Find:

The object distance

Solution:

The lens equation is given as

$\frac{1}{f}=\frac{1}{v} -\frac{1}{u}\\ \\ \frac{1}{20}=\frac{1}{40}- \frac{1}{u}\\\\\frac{1}{u}=\frac{1}{40} -\frac{1}{20}\\ \\u=-40cm$

The object should be placed at a distance of 40 cm.

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