Find the focal length and nature of lens which should be placed in contact with a lens of focal length `10 cm` so that the power of the combination becomes 5 dioptre.

a concave lens of focal length 20cm is placed in contact with a convex lens of focal length 40cm. Find the power of the combination.

Find the nature and focal length of a lens which must be placed in contact with a concave lens of focal length 25cm in order that the lens combination may produce a real image of an object placed at infinity.

A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is

A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination is

A convex lens of focal length 20 cm is placed in contact with a concave lens of focal length 10 cm. What is the focal length and power of the combination ?

A convex lens of focal length 40cm is in contact with a concave lens of focal length 25cm. The power of the combination is

A convex lens of focal length 25 cm is kept is contact with a concave lens of focal length 40 cm. What is the power of their combination ?

A convex lens of Focal length of 40cm is in contact with a concave lens of focal length 25cm. The power of the combination is.

What is the focal length of the combination if a lens of focal length - 70 c is brought in contact with a lens of focal length 150 cm? What is the power of the combination?