Question

State the condition when a lens is called an equi-convex or equi-concave.

• A. When radii of curvature of the two surfaces of lens are equal.
• B. When height of the two lens are equal.
• C. When radii of curvature of the two surfaces of lens unequal.
• D. None of the above

Answer 1

The correct option is A When radii of curvature of the two surfaces of lens are equal.

A lens is made up of two curved surfaces which can be concave or convex surfaces. When both the surfaces are of the same kind and have the same focal length, they form an equi-convex or equi-concave lens. For such lenses, the first and second principal focus will be at the same distance from the optical centre.