A convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses will be :

The power of a concave lens is 10 D and that of a convex lens is 6 D. When these two lenses are placed in contact with each other, the power of their combination will be :

The power of a converging lens is 4.5 D and that of a diverging lens is 3 D. The power of this combination of lenses placed close together is :

The optical prescription for a pair of spectacles is:

Right eye: - 3.50 D Left eye: - 4.00 D

(a) Are these lenses thinner at the middle or at the edges?

(b) Which lens has a greater focal length?

(c) Which is the weaker eye?

A person got his eyes tested by an optician. The prescription for the spectacle lenses to be made reads:

Left eye: + 2.50 D Right eye: + 2.00 D

(a) State whether these lenses are thicker in the middle or at the edges.

(b) Which lens bends the light rays more strongly?

(c) State whether these spectacle lenses will converge light rays or diverge light rays.