A convex lens has a focal length of 50 cm. Calculate its power.

Question

Question

This question was previously asked in

RRB ALP CBT I 29 Aug 2018 Shift 2 Official Paper

Answer 1

The correct answer is 2D

Key Points

A Convex lens converges incident rays towards the principal axis and is thin at the edges, and thick across the middle.
Focal length is the distance between the centre of a convex lens or focus where parallel rays converge.
The power of a convex lens is the ability of the lens to converge the rays that fall on it.
- The formula of Power is given by, \(P =\mathbf{ \frac{1}{f}}\) where 'f' is the focal length in meters.
- SI unit of Power is Diopter.
When the focal length, f = 50 cm i.e., 0.5 meters, the power is given by, \(P = \mathbf{\frac{1}{0.5}D = 2D}\). Hence option 3 is correct.

Additional Information

Convex lenses are used in microscopes, magnifying glasses, camera lenses and for the correction of hypermetropia.
Convex lenses have positive power as a convex lens has a positive focal length.
- The power of a concave lens is negative because a concave lens has a negative focal length.