Question

Which lens is converging?
A) An equi-concave lens or an equi-convex lens
B) An equi-concave lens
C) An equi-convex lens
D) Both A & B
E) Can’t say

Answer 1

Hint: Lens is a piece of transparent glass bound by two surfaces, concave as well as convex. In equi-concave and equi-convex lenses, both surfaces are of the same kind. Equi-convex lenses have the same radius of curvature on both surfaces, they also have positive focal length which produces real images.

Complete step by step solution:
Lenses are made up of two curved surfaces one of which can be concave or convex surfaces. When both the surfaces are of the same kind and have the same focal length, they are known as equi-convex or equi-concave lenses. For such lenses, the first and second principal focus is at the same distance from the optical centre.
Real images are formed when the lenses are converging.
Equi-Convex lenses have the same radius of curvature on the both surfaces. They also have positive focal lengths which makes them the optimum shape for producing real images. Equi-Convex lenses are the best when the object and image are at equal or near equal distance from the lens.

As equi-convex lenses form real images and real images are formed by converging lenses. Hence equi-convex lenses are converging. A converging lens means that the light rays converge after refraction.

Therefore, option B is the correct option.

Note: Lenses which are converging, converge the light rays after refraction. Converging lenses form real images on the opposite as that of the real object. Convex lenses are used to correct farsightedness, where the distance between the eye's lens and retina is too short, as a result of which the image is formed behind the retina.