# 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

### About N-Type and P-Type Semiconductor | Materials | Example |

Here you will know about  n type and p type semiconductor in details. You can already see about bonding in semiconductor . N type and P type semiconductor is used in electronic appliances.which is the basis of working of all the electronic devices.So lets discuss in this given topic in the details. N type and P Type Semiconductor When some impurities added to the pure semiconductor then it becomes extrinsic semiconductor and this process of adding impurities is known as doping.  Now it depends on the which type of impurities it added to the semiconductor (two types of impurities can be added to semiconductor pentavalent or trivalent). n-type semiconductor : If impurity that is added to the pure semiconductor is a pentavalent ( which has five valance electron ) then it is called n-type semi conductor. p-type semiconductor : If trivalent impurity is added to the semiconductor then it becomes p-type semi conductor. ( Note-List of  n type and p type semiconductor material is given below.

### Biasing of p–n Junction | Forward and Reverse-biased |

Biasing the p-n junction means applying some external voltage to both sides of the p-n junction. Reverse-biased junction and forward-biased junction are two types of biased junction. You should have also good understanding of  N-Type and P-Type Semiconductor before moving towards this topic. Biasing of p–n Junction  Biasing of a p–n junction  means uses of some external voltage across the two sides of the p–n junction. It is divided into two groups  Forward-biased junction :  When the p-side of junction  is connected to the positive terminal of a battery and the n-side of junction is connected to the negative terminal, the p–n junction is said to be a forward-biased junction.  Reverse-biased junction  :If the positive terminal of the battery is connected to the n-side of junction and the negative terminal on the p-side, the p–n junction is said to be a reverse-biased junction. Now we will see about forward and reverse-biased junction in detail.  Related Topic    Bonding in semiconduc

### Engineers Files Explained | Types of file

Today we will learn about engineers files explained, as we know hand tools are used to remove small amounts of material, usually from small areas of the workpiece.   Do you know why hand tools are used ?Hand tools are used because of following reason: If no machine is available,  The workpiece is too large to go on a machine  The shape is too intricate or simply that it would be too expensive to set up a machine to do the work. As you know the necessity of a hand tools now we will know about a hand tool , engineer's files. Engineer’s files Files are used to perform a variety of tasks, from simple removal of sharp edges to producing complex shapes where use of the device is impractical.Files can be obtained in a variety of shapes and in lengths from 150 mm to 350 mm. Single-cut file: When a file has a single series of teeth cut across its face it is called  single-cut file ,Figure of single-cut file is shown below. double-cut file: When a file has double series of teeth cut across