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

Image of Needle is real and inverted means this is real image it is 2f

Image is at a distance of 50 cm

Hence needle is kept 50 cm in front of convex lens.

Distance of object, u = – 50 cm.

Distance of image v = 50 cm

Focal length f = ?

As per lens formula.

P = \(\frac{1}{f(in\, mtr)}+\frac{1}{0.25}\) + 4D

f = 25 cm = 0.25 m

Power of the lens

Power of the lens P = + 4D.