Question

A convex lens forms a real & 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 size of image is equal to the size of the object. Also find the power of the lens.

Answer 1

Answer:

Object distance, u= – 50 cm

Image distance, v= 50 cm

Focal length = f

According to the lens formula,

u = -50 cm v = + 50 cm. f =? 1/f = 1/v €“ 1/u 1/f = 1/50 + 1/50 f = + 25 cm. = 0.25 m Power of lens (P) = 1/f = 1/ 0.25 = + 4D.

Answer 2

The position of the image should be at 2F since the image is the real and same size.

It is given that the image of the needle is formed at a distance of 50 cm from the convex lens. Therefore, the needle is placed in front of the lens at a distance of 50 cm