Coherent sources are defined as the sources in the which initial phase difference remains constant. In the case of two independent sources, the initial phase difference cannot remain constant because light is emitted due to millions of atoms and their number goes on changing in a quite random manner.

Coherent source of light are those sources which emit a light wave having the same frequency, wavelength and in the same phase or they have a constant phase difference.

In physics, two wave sources are perfectly coherent if their frequency and waveform are identical and their phase difference is constant. Coherence is an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference.

No, the two identical and independent sodium lamps do not act as coherent sources because the phase difference between waves emitted will change randomly and sustained interference will not be possible.

Sodium light has two wavelengths yet it is monochromatic because the distance between these two wavelengths is only 0.6 nm . In low pressure sodium lamp produce only yellow colour light but you can see a broader spectrum in high pressure.

Two independent sources of light (like two sodium lamps) cannot act as coherent sources. This is because millions of atoms are involved in the process of emission of light is each case and the process can be completely random.

Two independent monochromatic sodium lamps can not produce interference because.

In practice, a sustained interference pattern cannot be obtained by using two independent sources of light. It is because of the following reasons: Two independent sources of light can’t emit waves continuously. The waves emitted by two independent sources of light do not have same phase or a constant phase difference.

At the points where a crest and a trough meet together, both waves cancel out each other (interference minima) and where two crests or two troughs meet together, they reinforce each other (interference maxima).

Locating Local Maxima and Minima (Necessary Conditions) It states: Every function which is continuous in a closed domain possesses a maximum and minimum Value either in the interior or on the boundary of the domain. The proof is by contradiction.

Let S1 and S2 be two slits separated by a distance d. GG’ is the screen at a distance D from the slits S1 and S2. Point C is equidistant from both of the slits. The intensity of light will be maximum at this point because the path difference of the waves reaching this point will be zero.