Card # 53 Interference of light:
When there is a single coherent source of light, it will distribute light uniformly in all direction. If we have two coherent sources of light, which emits waves of same amplitude the distribution of light energy does not remain uniform in all direction. At the point where the crest of one wave falls on crest of other waves, resultant amplitude is maximum. At this point the intensity of light will be maximum. At that point, interference is said to be constructive. Otherwise it is destructive interference. In below figure, solid arc represents crest & dotted arc represents trough.
Young’s double slit experiment:
The experimental setup for Young’s double slit experiment is shown in the figure both 3D and 2D views have been shown below.
Experimental arrangement:
S is a narrow rectangular slit which is illuminated by a source of monochromatic light. The slit S acts as a line source for illuminating two narrow slits S1 and S2 lie very close to each other and at equal distance from source S. The wave fronts from S1 and S2 spreads out in all directions and in the region they superimpose on the screen, due to which alternate bright and dark fringes are observed. At the center of the screen, intensity of light is maximum and is called central maxima. The fringes disappear if one of the slits S1 or S2 is closed. Separation between the slits S1 and S2 = d,