When two or more light waves superimpose in the medium then according to the principle of superposition
the two waves added with each other. The resultant wave amplitude is equal to the sum or difference of
individual waves. It results variation of intensity in the region of superposition. This phenomenon is known
as interference. It can produce fringes or bands.
It is classified into two types.
a) Constructive Interference
b) Destructive Interference
A) CONSTRUCTIVE INTERFERENCE
When the resultant wave amplitude is equal to the sum of amplitude of individual waves then such
interference is known as constructive Interference.
B) DESTRUCTIVE INTERFERENCE
When the resultant wave amplitude is equal to the difference of amplitude of individual waves then such
interference is known as destructive Interference.
Conditions for interference
To observe interference phenomenon the following conditions should be required.
i. The light source should be coherent.
ii. The light source should have same wavelength and frequency.
iii. The distance between two light sources should be closer.
iv. The distance between two light sources and screen should be large.
v. To see interference fringes the background of the screen should be dark.
vi. The amplitude of the light waves should be equal or nearly equal.
vii. The sources should be narrow.