Find the focal length and nature of a 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.

Define focal length of a lens

A convex lens of focal lenth 30 cm and a concave lens of focal length 60 cm are placed in contact.Find the power of the combination.

What is the focal lengthof 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 ? Ignore thickness of the lenses.

Write expression for the focal length and power of a lens combination.

A lens is a focal length - 0.5 m. What is the nature and power of the lens?

What is the focal length of a convex lens of focal length 30cm in contact with a concave lens of focal length 20cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.