Diffraction of Light

Diffraction is defined as the bending of light waves around obstacles. As light wave passes through an opening, it spreads out. See figure below.


The amount of diffraction depends on the opening of the obstacle and the wavelength of the light wave. Maximum diffraction is possible through a small obstacle and long wavelengths. The smaller the opening, the greater the diffraction. The smaller opening, the lesser the diffraction. As the light passes through a very small opening, it serves as a point source of a new wave. It spreads out into new waves of light as it passes through an opening. Consider the figure below:


The vertical lines before the obstacle represent light waves. As these light waves pass through the opening in the obstacle, they bend on either side of the opening creating new waves represented by the curve lines. Thus, it become a point source of a new wave.

Example 1.

Light waves of equal wavelengths are passing through a barrier with opening of various sizes as shown in the figure below.  


Which opening would produce the 

a. greatest diffraction?

b. least diffraction?


a. As discussed, the diffraction produced depends on the opening where it pass through. The smaller the opening, the greater the diffraction. Based on the figure, C is the smallest opening, thus the greatest diffraction produced is in the opening C.

b. The bigger the opening, the lesser the diffraction produced. Opening D is the biggest opening, thus, it also produces the least diffraction.