Question

A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.

Answer 1

The object is placed at the centre of curvature for the convex lens, its image from the center of curvature, 2F2, is formed at a distance of 50 cm from the convex lens.

This placed in front of the lens and needle at a distance of 50 cm.

Object distance, u = −50 cm, Image distance, v = 50 cm, Focal length = f, According to the lens of power is+4D

Answer 2

HEY MATE, HERE IS UR ANSWER :-

Image distance (v) =+50cm

Since image is real and of same size. The positive of the image should be double the
focal length

By using v=2f

f=v/2

f=50/2= 25cm

Focal length of the lens is 25cm

power =1/f

=100/25 = 4D

power (P) of the lens is 4D

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