Question

an object is placed 20cm from the convex lens with the focal length 40 cm the image formed is virtual and erect what will be the power of the lens?​

Answer 1

Answer:

your answer is above.

I hope it will help you.

Answer 2

Given: An object is placed 20 cm from the convex lens with a focal length of 40 cm. The image formed is virtual and erect.

To find: The power of the lens.

Solution:

• When light rays parallel to the principal axis fall on a lens, they are bent towards the axis in a convex lens, and away from the axis in a concave lens.
• The more a lens bends the light rays, the greater is its power.
• The power of a thin lens is equal to the reciprocal of its focal length measured in metre.
• 40 cm is equal to 0.4 m.

        $P = \frac{1}{f}$

       $P = \frac{1}{0.4}$

           $= 2.5 D$

• The S.I. unit of the power of lens is dioptre (D).

Therefore, the power of the lens is 2.5 D.