Question

A convex lens and a concave lens of unknown powers are given to you. The lens of higher power is?
A) Always the convex
B) Always the concave
C) Determined by the nature of the image formed by lens
D) Determined by color of light used.

Answer 1

Hint: We are given two kinds of lenses but we do not know the individual powers. Power is defined as the reciprocal of focal length taken in metres. If we get to know about the focal length of the lenses then we would be able to tell the same.

Complete answer:
We know convex lenses are converging lenses and concave lenses are diverging lenses.
The focal length of a convex lens is always positive while the focal length of a convex lens is always negative.
Since, power is defined as the inverse of focal length taken in metres, the power of a concave lens will always be negative and the power of a convex lens will always be positive.
Thus, in any case the value of power of a convex lens will be greater than the concave lens.

So, the correct answer is “Option B”.

Note:
 Convex lens converges the light rays when incident on it while the concave lens diverges them all. The convex lens is bulgy in the middle while in the concave lens it is thin in the middle. The power is measured in units of Diopters, D. The combination of lenses can also be used to achieve the desired power.