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.

A man used a concave lens of focal length 20cm.Find the power of the lens.

Find the power of a convex lens of focal length 25 cm.

Calculate the focal length of the combination of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm. Is the system a converging or diverging lens?

a convex lens of power 3.5D is placed in contact with a concave lens of power -1.5D. Find the effective focal length of the combination.

When two thin converging lenses of focal lengths f, and f, are held in contact with each other, calculate the power of the combination.

Find the power of a concave lens of focal length 2 m ?