Question

In the double slit experiment, the pattern on the screen is actually a superposition of single slit diffraction from each slit and the double slit interference pattern. In what way is the diffraction from each slit related to the interference pattern in a double slit experiment? 

Explain. Hence draw the intensity distribution curve, obtained on the screen, in the double slit experiment 

(i) when the width of each slit is comparable to wavelength of monochromatic light used 

(ii) when the width of each slit is relatively large compared to wave length of monochromatic light

Answer 1

The pattern shows a broader diffraction peak in which there appear several fringes of smaller width due to the double slit interference. 

The number of interference fringes depends upon the ratio of the distance between the two slits to the width of a slit. 

In the limit of width of a slit becoming very small, the diffraction pattern will become very flat and we will observe the two slit interference pattern.