Which causes more bending (or more refraction) of light rays passing through it : a convex lens of long focal length or a convex lens of short focal length ?

An image formed on a screen is three times the size of the. Object. The object and screen are 80 cm apart when the image is sharply focused.

(a) State which type of lens is used.

(b) Calculate focal length of the lens.

The lens A has a focal length of 25 cm whereas another lens B has a focal length of 60 cm. Giving reason state, which lens has more power : A or B.

Name the physical quantity whose unit is dioptre.

Define 1 dioptre power of a lens.