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What is diffraction and explain the two types of diffraction???

What is diffraction and explain the two types of diffraction???

Grade:9

2 Answers

Anish Singhal
askIITians Faculty 1192 Points
5 years ago
Suppose there is a dark room, a completely dark room and through the window, there is a small hole. When light enters through that tiny hole, what happens? We see that through the small hole light enters but instead of just bright light, we see a region of light and dark bands. This is nothing but the diffraction of light.
Diffraction effect depends upon the size of obstacle. Diffraction of light takes place if the size of obstacle is comparable to the wavelength of light.
Diffraction of light can be divided into two classes:
Fraunhoffer diffraction.
Fresnel diffraction.


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https://www.askiitians.com/iit-jee-wave-optics/diffraction-and-polarization/#fresnel-and-fraunhofer-diffraction
Tony
108 Points
5 years ago
It is the bending of light around the corner of an obstacle. Reflected light produces fridges of light, dark or colored bands. At times diffraction of sunlight in clouds produces a multitude of colors. Example of diffraction in nature is diamond rays in the solar eclipse.
 
Diffraction
 
Types of Diffraction
There are two types of diffractions
 
Fresnel Diffraction
Fraunhofer Diffraction
Diffraction
 
From the above figure, we observe that the source is located at a finite distance from the slit, and the screen is also at a finite distance from the slit. The source and the screen are not very far from each other. So this is a Fresnel diffraction. Here, if suppose the ray of light comes exactly at the edge of the obstacles, the path of the light is changed. So the light bends a little and meets the screen.
 
A beam of width α travels a distance of α2/λ , called the Fresnel distance before it starts to spread out due to diffraction. But when the source and the screen are far away from each other, and when the source is located at the infinite position, then the ray of light coming from that infinite source are parallel rays of light. So this is Fraunhofer diffraction.
 
Here we have to make use of the lens. But why do we use the lens? Because in Fraunhofer diffraction, the source is at infinity so the rays of light which pass through the slit are parallel rays of light.
 
So in order to make these rays parallel to focus on the screen, we, make use of the converging lens. The zone which we get in front of the slit is the central mFresnel diffraction: produced when light from a point source meets an obstacle, the waves are spherical and the pattern observed is a fringed image of the object.
 
Fraunhofer diffraction: occurs with plane wave-fronts with the object effectively at infinity.axima. On either side of central maxima, there is bright zone i.e 1st maxima.
 
Fresnel diffraction: produced when light from a point source meets an obstacle, the waves are spherical and the pattern observed is a fringed image of the object.
 
Fraunhofer diffraction: occurs with plane wave-fronts with the object effectively at infinity.

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