- Sustained interference means positions of maxima and minima of light intensity remain fixed throughout the screen.
- The intensity of the light remains same throughout.
- In case of sustained interference the phenomenon of interference is permanent.
- Therefore sustained interference is also known as permanent interference.
Conditions for sustained interference:-
- Sources should be coherent.
- If the sources are not coherent then there will no fixed pattern of constructive and destructive interference.
- Sources should be very close to each other.
- Sources should be point sources.
- If the sources are not point then the distinction between bright and dark bands won’t be clear.
- Amplitudes from sources should be equal.
- If amplitudes are not same then the intensity of the pattern formed will also vary. It won’t be fixed.