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What is Coherence | Types and Example |

What is Coherence in physics ?

Do you searching about what is coherence ? According to physics definition of coherence  When two or more electromagnetic waves are said to be coherent, their frequency is the same and they are in phase or maintain a steady phase difference with them. In general, the phase may vary from one point to another or may change from time to time.To generate interference, coherent light sources are required. The concept of coherence is explained below.

coherence physics

Types of  Coherence 

We have two distinct coherence, namely (i) temporal coherence and (ii) spatial coherence.

(i) Temporal coherence This refers to the correlation between the field of a wave at one point at some point and the field at the same point at a later time.Temporal coherence is refers only a single beam of light

(ii) spatial coherence If there is a constant phase difference in the space between the waves at different points for a time t, they are called spatial coherent.It refers  the relationship between two separate beams of light.

what are example of coherence ?

1. Laser light -  Laser light is an example of a coherent light source. The light emitted by the laser light has the same frequency and phase.

2. Sound waves - Sound wave are another example of coherent sources. The electrical signals of the sound waves travel with the same frequency and phase.

Interference in thin films by reflection

When white light (sunlight) falls on thin films such as soap bubbles or air films, beautiful colors will appear due to interference. The interference of light in thin films can be explained by allowing monochromatic illumination of wave length λ ′, which can fall on a thin film of thickness ′ t, as shown in the given figure. Let the refractive index of film material be material μ .

AB is a monochromatic incident light beam at "B" in an equally thick transparent film. A portion of the beam is reflected along BC and the remaining light is refracted with BD. A portion of the refracted ray is reflected with D in "D". Then, this beam refracts with EF at "E" and enters the air. Re BC and EF are parallel and overlap to produce interference. The intensity of the interference fringe depends on the path difference between BC and EF rays. The path difference "path" is given below

Interference in thin films by reflection
Interference in thin films by reflection


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