## What is the basic principle of air wedge experiment?

The phase difference between the two rays is used to get interference fringes. It’s alternative light and dark fringes. The path difference between the rays has to be equal.

## What is meant by air wedge?

Air Wedge. An air wedge is a simple interferometer used to visualize the disturbance of the wave front after propagation through a test object.

## How do we get fringes using an air wedge?

If two glass plates are placed face to face with one end separated by a piece of tissue paper or thin metal foil an air wedge will be formed between them. If monochromatic light is shone on the plates a series of straight-line fringes will be seen parallel to the line along which they touch (Figure 1).

## Why the center of Newton’s ring is dark?

The central fringe in Newton’s rings is dark in the case of the reflected system because the air film thickness formed at the centre between the glass plate and the lens is zero. Hence, at the geometrical path difference between the incident and reflected rays from the glass plate is zero.

## Why do we get circular fringes in Newton rings?

The path difference between the reflected ray and incident ray depends upon the thickness of the air gap between lens and the base. As the lens is symmetric along its axis, the thickness is constant along the circumference of a ring of a given radius. Hence, Newton’s rings are circular.

## What is principle of Newton’s ring?

Newton’s rings is a phenomenon in which an interference pattern is created by the reflection of light between two surfaces; a spherical surface and an adjacent touching flat surface. It is named after Isaac Newton, who investigated the effect in his 1704 treatise Opticks.

## On what factors does the diameter of ring depend?

Ans: Diameter of a ring depends on the wavelength of light used, refractive index of the medium between lens and glass plate, order of the ring and radius of curvature of Planocovex lens.

## What are the factor which govern the radius of ring?

Ans. The radius depends upon (i) wavelength of light used. (ii) refractive index ‘μ’ of enclosed film. (iii) radius of curvature R of convex lens.

## Why do the rings get closer as the order of the Rings increases?

Rings get closer as the order increases (m increases) since the diameter does not increase in the same proportion. In transmitted light the ring system is exactly complementary to the reflected ring system so that the centre spot is bright. Under white light we get coloured fringes.