Condition for obtaining clear and broad interference bands
(i) The screen should be as far away from the source as possible.
(ii) The wavelength of light used must be larger.
(iii) The two coherent sources must be as close as possible.
Observable interference can take place if the following conditions are fulfilled:
(a) The two sources should emit, continuously, waves of some wave-length or frequency. While deriving conditions for maxima and minima, we have taken ‘I’ for both the waves to be same.
(b) The amplitudes of the two waves should be either or nearly equal. A good contrast between a maxima and minima can only be obtained if the amplitudes of two waves are equal or nearly equal.