Question

To demonstrate the phenomenon of interference we require two sources, which emit radiations of

• A. Two sources that emit radiation of the same frequency
• B. Two sources that emit radiation of nearly the same frequency
• C. Two sources that emit radiation of the same frequency and have a definite phase relationship
• D. Two sources that emit radiation of different wavelengths

Answer 1

The correct option is C

Two sources that emit radiation of the same frequency and have a definite phase relationship

Explanation for Correct Option:

Option (C):

1. An important consequence of the principle of superposition is that when two beams of light intersect, the propagation of each beam is completely unaffected by the presence of the other.
2. However, in the region of crossing both the beams act simultaneously and we expect a change in intensity.
3. A case of utmost importance occurs when monochromatic waves of light from two sources proceed almost in the same direction and superpose at a point either in the same or in the opposite phase.
4. Then the intensity of light at that point will be maximum or minimum according to whether the waves meet the point in the same or in the opposite phase.
5. This phenomenon is known as interference of light.
6. Hence, for interference to occur we require two coherent sources of light.
7. Coherent sources are when two light sources have the same frequency and phase difference.
8. This can be achieved by allowing light from a point source to pass through two equal slits.
9. Therefore, to demonstrate the phenomenon of interference we require two sources, which emit radiations of the same frequency.

Explanation for Incorrect Options:

Option (A):

1. From the above explanation, we can see that for interference to occur we require two coherent sources of light.
2. Coherent sources are when two light sources have the same frequency and phase difference.
3. Therefore, to demonstrate the phenomenon of interference we do not just require two sources, which emit radiations of the same frequency.

Option (B):

1. From the above explanation, we can see that for interference to occur we require two coherent sources of light.
2. Coherent sources are when two light sources have the same frequency and phase difference.
3. Therefore, to demonstrate the phenomenon of interference we do not require two sources, which emit radiations of nearly the same frequency.

Option (D):

1. From the above explanation, we can see that for interference to occur we require two coherent sources of light.
2. Coherent sources are when two light sources have the same frequency and phase difference.
3. We know that frequency is inversely proportional to wavelength.
4. Therefore, to demonstrate the phenomenon of interference we do not require two sources, which emit radiations of different wavelengths.

Hence, the correct answer is option (C).