# Wave Interference – Short Questions With Answer | Physics Class 12

## Physics | Solved Questions Wave Interference – Short Questions With Answer Class: 12

1. Can two independent sources of light produce interference?
Ans. Two independent sources cannot be coherent because: Light is emitted by individual atoms and not by the bulk of matter acting as a whole. Even a tiniest source consists of millions of atoms, and emission of light by them takes place independently. Even an atom emits an unbroken wave of above 10-8 second due to its transition from a higher energy state to a lower state.

AS a result of above factors, the phase difference between two independent light sources changes after very 10-8 second. So, the position of maxima and minima of intensity will change about 10-8 times in one second. Such rapid changes cannot be seen by our eyes and almost a uniform illumination on the screen is observed. Hence, two independent light sources cannot produce a sustained interference pattern.

2.Why have the two sources of light to be close to each other for the production of good interference pattern?
Ans. The two source of light should be close to each other for the production of good interference. This is so because in interference, the fringe width (β) is inversely proportional to the distance (d) between coherent sources. So, if d is very small. We can distinguish one fringe of inference pattern from its other fringe.

3. Distinguish between interference and diffraction.
Ans. The difference between interference and diffraction are as follows:

 Diffraction Interference It is the phenomenon of interaction of light coming from different parts of the same wave front. It is the phenomenon of interaction of light coming from two different wave fronts originating from two coherent sources. Diffraction fringes are not of the same width. Interference fringes may or may not be of the same width. Points of minimum intensity are not perfectly dark. Points of minimum intensity are perfectly dark. All bright bands are not of the same intensity. All bright bands are of uniform intensity.

4. What do you understand by coherent source?
Ans. Coherent source are sources which emit waves of the same frequency and possess a constant phase difference (i.e phase difference remains constant with time). Since two independent sources can never be coherent so coherent sources are obtained from a source by division of wave front or division of amplitude techniques.

5. In Young’s double slit experiment, how is the fringe width altered if the separation between the slits is doubled and the distance between the slits and the screen is halved?
Ans. The fringe width is given by the relation β = λD/d,
Where λ, D and d are the wavelength of light, distance of the screen from the slits and the separation between the slits respectively.

Now, according to the question, d1 =2d and D1 =D/2

Therefore B1 =λD1/d1 = (λ/2 × 2d) × (β/4) = ( 1/ 4)

Hence, the fringe width decreases to of its value.

5. What should be the path difference between two interfering waves for constructive interference and destructive interference?
Ans. In constructive interference, the path difference between two interfering waves should be integral multiple of wavelength λ.

i.e. x=nλ where n= 0,1,2,3,………………

Similarly, in destructive interference, the path difference between two interfering waves should be an odd half-integral multiple of wavelength λ. i.e. x= (2n + λ1/2) where n=0,1,2,……………

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Posted August 19, 2015 at 12:39 am

This is too good for us. So congrach but can you send questions and answer in only hindi please.

Posted August 19, 2015 at 12:43 am

Say can you give me questions with answer in hindi? Tell me now

• MeroSpark
Posted August 19, 2015 at 10:18 am

We have posted Questions Solution in this site. You can able to choose “Solved Questions” from Tag Cloud. We haven’t this notes on Hindi format. Thank you for visiting us.