What is interference? Write the condition for path difference in case of constructive and destructive interference?

Hint: To understand interference patterns one must be summarized by two conditions; in interference the source of the wave should be coherent, I-e they must emit identical waves with a constant phase difference. The waves should be monochromatic-they should be of a single wavelength.

Complete answer:
INTERFERENCE: A phenomenon is said to be interference in which two waves are coherent to each other, superpose to form a resultant wave of greater, lower or same amplitude. In other words we can also say that when two or more waves simultaneously and independently travel through the same medium at same time, that effects are super positioned and the result of super positioned is known as interference.

THERE ARE TWO TYPES OF INTERFERENCE:

(i)CONSTRUCTIVE INTERFERENCE: This type of interference occurs when the wave amplitudes reinforce each other by building a new wave of even greater amplitude.

(ii)DESTRUCTIVE INTERFERENCE: This type of interference occurs when the wave amplitude opposes each other by resulting in waves of reduced amplitude.

For the waves to superimpose constructively, path difference between two waves must be integral multiple of wavelength of wave i-e. $\Delta x = n\lambda $

For the waves to superimpose destructively, the path difference between two waves must be half- integral multiple of wavelength of wave i-e. $\Delta x = (n+\dfrac{1}{2})\lambda $

USES OF INTERFERENCE:

(a.)It is used for testing surface qualities; roughness of surface, spherical surface etc..
(b.)Space applications which includes; radio-astronomy.


Note: The superposition is the main principle used in interference of light. The superposition says that when the incoming light waves superimpose constructively, the intensity increases whereas when they add to destructively it decreases. The soap bubble, a thick film, wedge shaped film all somehow shows the interference pattern.