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# Physics Practical Class 12 - To find the focal length of a convex lens by plotting graphs between u and v or between 1/u and 1/v. Viva Questions with Answers

1) What is an optical aberration?

The property of the lens that causes blurriness or distortion during the formation of an image is known as an optical aberration. The light is spread out or dispersed due to optical aberration rather than being focused on a certain fixed point. Optical aberration is an unwanted property of the lens, and by using a grouping of lenses rather than using a single piece of the lens, it can be eliminated.

2) What is magnification?

Magnification of the lens is basically the ratio of the linear size of the image to the linear size of the object.

m = (linear size of the image/linear size of the object)

3) What is a convex lens?

A lens that is curved outwards is known as a convex lens. Convex lenses are also known as converging lenses. The thickness at the centre of a convex lens is more than its edge. A convex lens has the capability to converge a parallel beam of light into a point.

4) What is a concave lens?

The type of lens with at least one side curved inwards is known as a concave lens. A Biconcave lens is a concave lens with both sides curved inward. Concave lenses are also known as diverging lenses because they spread out or diverge the rays of light that are refracted through it.

5) Define the power of a lens?

The measure of the ability of a lens to converge or diverge the incident beam of light is known as the power of a lens. It is given by the reciprocal of focal length.

6) What is chromatic aberration?

Dispersion is the reason why chromatic aberration occurs. Due to chromatic aberration, a lens fails to focus all colours on the same point, and colourful fringes around an image can be observed due to chromatic aberration. An achromatic doublet can be used to fix chromatic aberration.

7) Define refraction.

Refraction is basically the bending of light when it passes from one medium to another. Several devices, like microscopes, corrective lenses, magnifying lenses etc., use this property of refraction. In this property, the polarisation of electrons takes place when the light is transmitted through a medium, which in turn decreases the speed of light; therefore, the direction of light changes.

8) What is total internal reflection?

When the light rays travel from a more optically denser medium to a less optically denser medium, the phenomenon that happens is known as total internal reflection.

9) What are optics, and what are their types?

The study of the wave properties of light is known as optics, and it is divided into three categories:

• Diffraction
• Interference
• Polarisation

10) What is wave optics in physics?

The branch of optics that studies the phenomena for which the ray calculation of geometric optics is not valid, like interference, diffraction, polarisation, and others, is known as wave optics.