Focal length of the plano – convex lens is …………… when its radius of curvature is R and n is refractive index of the lens.

If 40 cm each is the object and image distance respectively for a convex lens then the focal length is ………

If a convex lens has its ob j ect and image distance equal (say x) the focal length is equal to …………

If the image distance of a convex lens of focal length 25 cm is 75 cm then the object distance is …………

An image is formed at a distance of 60 cm from the centre of a convex lens when the object distance is 30 cm. The focal length of the lens is ………

An image is formed at distance of 30 cm from the centre of convex lens of focal length 15 cm. The distance of the object is ………

Air bubble in water behaves like a diverging lens because …………

A magnifying glass forms ………

Among the following cases the image formed by a convex lens is real.

Among the following cases the image formed by a convex lens is not real.

A convex lens of focal length 20 cm is cut into two halves along principal axis then focal length of each part will be ………

A convex lens of focal length 20 cm is cut into two halves perpendicular to the principal axis then focal length of each part will be ………

We can’t discuss the size and nature of the image formed while using a convex lens, when the object is placed ………

For a given spherical lens the paraxial rays …………

Which of the following is true?