Interferece

Question 1

What are the conditions for sustained interference?

Answer 1

1. The two sources should continuously produce light of the same wavelength.
2. The amplitudes should be equal or nearly equal for good contrast.
3. The sources should be narrow.
4. Two sources should be close to each other.
5. The two sources should be coherent both spatially and temporally.

Question 2

What do you mean by interference by division of wavefront?

Answer 2

It is the process of obtaining the interference patterns by making the different parts of the same wavefront along different paths, only to recombine them at last to produce interference. Since they are part of the same wavefront, the condition of coherence is satisfied. The condition of narrow sources is obtained using Fresnel’s biprism and Lloyd’s mirror.

Question 3

What do you mean by the division of amplitude? What categories of interference belong to it?

Answer 3

This is another method of obtaining interference by dividing the amplitude of the wavefront and making the separate amplitudes go separate ways and recombine at last to produce interference. It is obtained by using thin films and Newton’s ring apparatus.

Question 4

What is the concept of intensity of a wave?

Answer 4

The intensity of a wave is directly proportional to the square of amplitude.

Question 5

What is the Stokes law of phase change?

Answer 5

In the absence of any absorption, a light ray that is reflected or refracted will retrace its original path if its direction is reversed.This has implication that when light gets reflected from denser medium, it suffers phase change of 180 degree.

Question 6

What is Rayleigh’s condition?

Answer 6

For the two different spectral lines to form a bright interference, the nth order of the longer wavelength should be equal to the n + 1 order of the shorter wavelength.

Question 7

what are the uses of the following parts of the Michaelson Interferometer?
1. Collimating lenses
2. Polished plate
3. Unpolished plate
4. Mirror

Answer 7

1. Collimating lens: To produce parallel beams of light from the source.
2. Polished plate: The polish helps to reflect half of the light and transmit half of the light.
3. Unpolished plate: To equalize the path difference between the two lights.
4. Mirror: To reflect the light to help recombination.

Question 8

What are the conditions for the formation of circular fringes and localized fringes in the Michaelson interferometer?

Answer 8

Localized fringes: The mirror should be inclined to one another.
Circular fringes: The mirror should be perpendicular to one another.

Question 9

What are the applications of Michaelson’s interferometer? Derive the expression for those applications.

Answer 9

The applications are given in the book. If you don’t know, refer to that.

Question 10

How does the thin wedge film produce path difference? And what is the path difference? Why?

Answer 10

The path difference is shown in the figure.

Question 11

How is the standardization of a meter done using the Michaelson interferometer?

Answer 11

Please update the answer here once you know it.

Question 12

What is an etalon?

Answer 12

An etalon is a sub-standard for length and consists of two mirrors that are plane-paralleled and highly silvered on their front surfaces.

Question 13

What is the formula for path difference in Michaelson’s interferometer?

Answer 13

2dcos(theta) = n(lambda) for maximum
= 2n+1 times half of lambda for minima

Question 14

What is the formula for path difference in the Febry-Perot interferometer?

Answer 14

Same as Michaelson’s interferometer.

Question 15

What is the superiority of the Febry-Perot interferometer over Michaelson’s interferometer?

Answer 15

When light consists of two close wavelengths, each wavelength produces its pattern in a Fabry-Perot interferometer.

Question 16

Why are reflection boundaries specified as ordered pairs?

Answer 16

Because the wave’s phase changes by 180 denser when they are reflected by a denser medium. Thus we can keep track of the phase change when we specify the reflection boundary as an order pair.

Question 17

What is reflection phase change?

Answer 17

When a wave gets reflected by a denser medium, its phase changes by 180 degrees. This is called reflection phase change.

Question 18

Reflection from which face of the planoconvex lens is not considered when drawing Newton’s ring experiment ray diagram?

Answer 18

The reflection from the plane mirror is not considered. And the reflection is one like that of wedge film.

Question 19

What is the path difference in Newton’s ring experiment?

Answer 19

2utcosr - half of lambda

Question 20

What are the applications of Newton’s ring?

Answer 20

1. To determine the wavelength of sodium light
2. To determine the refractive index of the liquid.

Question 21

What is the condition of obtaining a bright center at Newton’s ring?

Answer 21

The condition is that a liquid should be placed in place of an air film whose refractive index is more than that of a glass plate but less than that of a planoconvex lens.

Question 22

State the application of Michaelson’s interferometer and then explain the theory and process behind the application.

Answer 22

Refer to the book if you don’t know.

Question 23

Why are the inner surface and outer surface of the Fabry-Perot interferometer not parallel?

Answer 23

To avoid interference effect due to multiple reflections and refractions

Question 24

Why is the Fabry-Perot interferometer useful for resolving small wavelengths?

Answer 24

Because the ring pattern of the Fabry-Perot interferometer is extremely sharp. Please fill in the why and how by reading further. Now, this is not necessary so I am leaving it for now.

Question 25

What is the relation of mirrors’ distance d between Fabry-Perot interferometer, and the fringe width?

Answer 25

As the mirrors come closer, the fringes shrink and disappear at the center. A decrease in half of the wavelength results in the collapse of one ring in the center.