Question

Which of the following is not essential for two sources of light in Young's double slit experiment to produce a sustained interference?
A) Equal wavelength
B) Equal intensity
C) Constant phase relationship
D) Equal frequency

Answer 1

Hint
To obtain the effect of optical phenomena like interference in a lab, we need coherent sources of light. This is the essential condition without this we can’t observe the interference pattern.

Step by step solution
Two equivalent slits lighted by a laser beam can be said to be two coherent sources.
Further there are following conditions for the interference of light: the sources of light must be constant, which emits similar waves with constant phase difference. The wave must be monochromatic, they must have a single wavelength.
1. Coherent sources of light
2. The amplitude of waves must be equal to make a good contrast between maxima and minima.
3. To be considered the point source of light, the source must be small.
4. To produce wide fringes, the sources must be close to each other.
5. To produce the wide fringes the distance between source and screen should be large.
6. The sources must produce the light in the same state of polarisation.
7. The sources must have a single wavelength or we can say that they must have the same frequency.
Hence, intensity is not the essential condition for the sustained interference pattern.
Therefore, option B is correct.

Note
When two light waves from different coherent sources are combined, the energy distribution due to one wave is distributed by another. This change in light distribution is known as interference of light, due to superposition of two light waves.