what is Diffraction
In this section we will understand what is diffraction and how does it affect wave propagation. definition of diffraction is given as the bending of a wave due to some obstacle in its path or its spreading after passing through small gaps or apertures.
Diffrction is observed when an obstacle comes in the path of the waves. The objects or obstacles that come in the way are known as diffracting or obstructing objects. Diffrction is more effective if the wavelength of the wave is approximately equal to the size of obstacle. If the diffracting object has many closely spaced gaps in it then a complex pattern is formed which has variable intensity. This variation is a result of interference occurred between different parts of the wave that propagates by different ways.
diffraction equationConsider two rays which pass through opening and make angle Ө with the straight through line. Constructive interference will occur if the difference in their path lengths is an integral multiple of their wavelength. Path difference="nλ" where n = 1,2,3,...dsinӨ=nλd is the width of slit, n is an integer 0. Diffrction can be observed in everyday life also. For example when we look at a CD or DVD then the closely spaced tracks on it forms a pattern of rainbow. This can also be seen on the hologram of ATM card etc.
sound wave diffraction is also observed when a person calls another person behind a tree then the other person is able to hear that sound. This is due to diffrction phenomenon of the sound wavediffraction of sound wave with longer wavelength or low frequency is more effective than a wave of shorter wavelength. As shown in the diagram below sound diffrction occurs when the sound waves bend around a post (obstacle in this case for sound wave).
For this to happen wavelength of sound should be long enough or the size of the obstacle (post) should be small in comparison to the wavelength. If you are at a distance equal to several wavelengths of sound wave then you will not observe the affect due to the post. Again sound diffrction occurs when you are outside a door and you are able to hear sound coming from inside. This happens due to spreading of sound wave through small opening. Diffrction affects when a sound proof room is made. For such cases we need to ensure that there is no opening left at the walls of the room. Any opening can cause diffrction (spreading) of sound through it.