Conditions for Sustained Interference of Light Waves
The following are the conditions for sustained interference of light waves:
- The two sources of light should be coherent that is they should aim at light waves having a sharply defined phase difference that remains constant with time. This is necessary for a sustained interference pattern.
- The waves emitted by the two sources should have the same frequency. if waves have different frequencies the phase difference between them will continue very and the resultant intensity at any point will change with time.
- The principle of superposition must be followed.
- The separation between the light source should be as small as possible. if d is large the fringes with it will be very small and fringes will not be separately visible.
- The distance of the screen from the two sources should be quite large. this is also necessary to obtain widely spaced fringes.
- The amplitude a1 and a2 of the interfering waves should be equal or very nearly equal. This is necessary for better contrast. If a1 and a2 are wildly different there will be little difference between the intensities of bright and dark fringes that is the contrast between them will be poor. The maximum contrast will be obtained when the level equals a2 because then dark fringes will have zero intensity.
- The light should be monochromatic otherwise there will be overlapping of fringes and there will not be clarity in the interference pattern.