# Introduction to diffraction

In general, the curvature of the waves around the edges of the barriers is known as the diffraction. The amount of flex depends on the wavelength of the waves and the size of the barrier. Bending is great in case of sound waves due to long waves. Light waves also bend to a smaller degree [due to shorter wavelengths], as they pass through sharp edges of obstacles or narrow openings. The curvature of light waves is more pronounced when the size of the aperture is equal to the wavelength of the light.

 Diffraction at straight edge

## What are the different types of diffraction ?

According to Fresnel, the diffraction is due to the interference of the different secondary waves originating from the wavefront that are not obstructed by the obstacle. The diffraction phenomena are divided into two classes, they are (i) the Fresnel diffraction and (ii) the Fraunhofer diffraction.

(i) Fresnel diffraction - In such diffraction, the light source and screen diffraction are at a finite distance from the opening or barrier that has a sharp edge. The incident wave at the opening or barrier is spherical or cylindrical.

(ii) Fraunhofer diffraction: In such diffraction, the light source and the screen are infinitely far from the opening or barrier of the diffraction that has a sharp edge. This can be accomplished by placing the light source in the focal plane of the convex lens and display in the focal plane of the second convex lens. In this case, the wavefront event at the opening or barrier is a flat wavefront.

### Fraunhofer Diffraction

1.The point light source or an illuminated narrow slot is  used as the light source.

2.The light incident on the opening or barrier is spherical or cylindrical wave front .

3.Lenses are not used to focus the rays
1.Extended light source at infinite distance used as a light source

2.The incident light in the opening or obstacle is a plane wave front.

3.Converging lens is used to focus the rays

### 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.
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