Interference According to the Dictionary:

• The process in which two or more light, sound, or electromagnetic waves of the same frequency combine to reinforce or cancel each other, the amplitude of the resulting wave being equal to the sum of the amplitudes of the combining waves.
• In Physics interference is a phenomenon in which two waves superimpose to form a resultant wave of greater, lower, or the same amplitude. Interference usually refers to the interaction of waves that are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency. Interference effects can be observed with all types of waves, for example, light, radio, acoustic, surface water waves or matter waves.
• Interference is the phenomenon that occurs when two waves meet while traveling along the same medium.
• The interference phenomena were experimentally demonstrated by Thomas young in 1801. Due to interference, we will observe many observations in our daily life, such as  multiple colors on soap bubbles as well as on oil film when viewed under sunlight .
• The concept of Interference was best explained on the basis of superposition of waves.

Principle of Superposition of  waves:

Definition :

• The resultant displacement of two or more waves traveling simultaneously in a medium at any point is equal to the algebraic sum of the displacements due to individual waves.
• To understand this concept , Let us  consider two waves traveling simultaneously in the medium. Let$$ Y_{1}$$ and $$Y_{2}$$ are the displacements of  the first and second at any point in the absence of  each other.
• According to principle of superposition, the resultant displacement (Y) of two waves is given by Y =   $$Y_{1} \pm Y_{2} $$
• When two waves are in same phase, their resultant amplitude is Y = $$Y_{1} + Y_{2}$$

• When two waves are in opposite phase, their resultant amplitude is Y = $$Y_{1} – Y_{2}$$

Conditions for Interference :

• Two light sources of emitting light waves should be coherent.
• Two sources must emit continuous light waves of same wavelengths or frequency
• The separation between the two sources should be small.
• The distance between the two sources and the screen should be large.
• To view interference fringes, the background should be dark.
• The amplitude of light waves should be equal or nearly equal.
• The sources should be narrow.
• The sources should be monochromatic.( Monochromatic light refers to light that is of one color, since it only emits one color, monochromatic light has a single wavelength).