Question

Which of the following quantities is inside the lens?
A. Focal length
B. Radius of curvature
C. Optic centre
D. Power

Answer 1

As a first step, one could give a brief description about optical lenses. Then you could list down all the physical quantities related to it. You could also list down the properties related to a lens. Among the given options, find out that quantity whose position is inside the lens.

Complete step-by-step solution:
In the question we are given certain physical quantities that are directly related to the lens.
Let us first give a brief description of a lens. A lens is known to be that transmissive optical device that could focus as well as disperse a light beam by virtue of refraction. We have simple lenses as well as compound lenses. When the lens consists of a single piece of transparent material, it is a simple lens and when the lens consists of several such lenses stacked along a common axis, it is a compound lens.
Now, there are many physical parameters that are related to a lens like: radius of curvature, power, focal length, refractive index etc. Refractive index and power are all basically the properties of a lens as in we could calculate the value but we cannot physically represent it. But focal length, radius of curvature, etc are measurable lengths of great significance related to lenses. Among the given options, the optical centre is that quantity that is present inside the lens.
Hence, option C is correct.

Note: Telescopes, binoculars and cameras all need lenses in its basic structure. What we should understand is that a lens can focus light so as to form an image unlike prisms which simply reflects off the light. Another application of lenses are as visual aids in glasses so as to correct defects related to vision.