Question

The power of convex lens is:
A. Negative
B. Positive
C. Zero
D. Imaginary

Answer 1

Lens is an object that converges or diverges the light passing through it. There are two types of lenses, convex and concave lenses. A convex lens is bulged out and the concave looks like a cave on both sides.

Complete step by step answer:
Various quantities define the property of a lens or its working, like focal length, object distance, and image distance. These values are considered along with sign convention. Considering the normal cartesian sign convention, the focal length of the convex lens is positive as its first spherical surface will have a focus on the right-hand side of the pole.
The power of the lens is defined as the reciprocal of the focal length of the lens. For convex focal length is positive so power will also be positive.

So, the correct answer is “Option B”.

Note:
The focal length of the concave lens is negative as the focus of the first spherical surface lies on the left-hand side of the pole.
The power of the concave lens is negative because its focal length is negative and power is the reciprocal of the focal length.
When light rays pass through the convex lens, they converge at the focus of the lens. But, when a light ray passes through the concave lens they diverge and when they are produced backward they met at its first focus.
Basic laws to make the ray diagram for a lens are, a ray passing parallel to the principal axis will pass through the focus on the other side, and rays passing through the focus will become parallel on the other side.