Question

Sustained condition for diffraction

Answer 1

To obtain well defined interference patterns, the intensity at points corresponding to destructive interference must be zero, while intensity at the point corresponding to constructive interference must be maximum. To accomplish this the following conditions must be satisfied.

The two interfering sources must be coherent, that is, they must keep a constant phase difference.The two interfering sources must emit the light of the same wavelength and time period. This condition can be achieved by using a monochromatic common original source, that is, the common source emits light of a single wavelength.The amplitudes or intensities of the interfering waves must be equal or very nearly equal so that the minimum intensity would be zero.The separation between the two coherent sources must be as small as possible so that the width (D ?/2 d) of the fringes is large and are separately visible.The two sources must be narrow or they must be extremely small. A broad source is equivalent to a large number of fine sources. Each pair of fine sources will give its own pattern. The fringes of different interference patterns will overlap.The distance between the two coherent sources and the screen must be as large as possible so that the width of fringes (D ? /2 d) is large and are separately visible.The two interference waves must be propagated along the same direction so that their vibrations are along a common line.