Question

Kiran wants to focus a light beam behind the lens but as nearer to the optical centre of the lens as possible. Which lens kiran would choose in order to do so?

• A. Thin convex lens
• B. Thick convex lens
• C. Thin concave lens
• D. Thick concave lens

Answer 1

The correct option is B Thick convex lens

Power of a lens is its converging/diverging power. More precisely for a convex lens more is the power more will be its converging ability. Also power is inversely proportional to focal length of a lens. Hence in order to converge the light beam nearer to the lens, focal length of the lens should be as minimum as possible.
Focal length and hence power depends upon the width of the lens. More is width, more will be its power and hence lesser will be focal length.