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Diffraction

The bending of light waves around the corners of an obstacle or aperture is called diffraction of light.

The phenomenon of diffraction is divided mainly in the following two classes

(a) Fresnel class
(b) Fraunhofer class

S.NoFresnel ClassFraunhofer Class
1The source is at a finite distanceThe source is at infinite distance
2No opticals are required.Opticals are in the form of Collimating lens and focusing lens are required.
3Fringes are not sharp and well defined.Fringes are sharpend well defined.


Fraunhofer Diffraction at a Single Slit

Linear Width 0f central maximum 2Dλ / a = 2fλ / a

Angular width of central maximum = 2λ / a

where, λ = wavelength of light, a = width of single slit, D = distance of screen from the slit and f = focal length of convex lens.

For Secondary Minima

(a) Path difference = nλ

(b) Linear distance = nDλ / a = nfλ / a

(c) Angular spread = nλ / a

where, n = 1, 2, 3,.,.

For Secondary Maxima

(a) Path difference = (2n + 1)  λ/ 2

(b) Linear distance = (2n + 1) Dλ / 2a   = (2n + 1) fλ / 2a

(c) Angular spread = (2n + 1) λ / 2

 Important Points

  • A soap bubble or oil film on water appears coloured in white light due to interference of light reflected from upper and lower surfaces of soap bubble or oil film.
  • In interference fringe pattern all bright and dark fringes are of same width,
  • In diffraction fringe pattern central bright fringe is brightest and widest. and I remaining secondary maxima's are of gradually decreasing intensities.
  • The difference between interference and diffraction is that the interference is the superposition between the wavelets coming from two coherent sources while the diffraction is the superposition between the wavelets coming from the single wavefront
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FAQs on Single Slit Interference & Diffraction Pattern - Physics for ACT

1. What is single slit interference and diffraction?
Ans. Single slit interference and diffraction is a phenomenon that occurs when light passes through a narrow slit, creating an interference pattern on a screen. It is caused by the bending and spreading of light waves as they pass through the slit, resulting in the formation of bright and dark fringes.
2. How does the width of the slit affect the interference and diffraction pattern?
Ans. The width of the slit plays a crucial role in determining the interference and diffraction pattern. A narrower slit will result in a wider and more spread-out pattern with narrower fringes, while a wider slit will produce a narrower pattern with wider fringes. This is because the narrower the slit, the more the light waves diffract and interfere with each other.
3. What is the difference between interference and diffraction in the context of single slit patterns?
Ans. Interference refers to the phenomenon where two or more light waves combine to either reinforce or cancel each other, resulting in the formation of bright and dark fringes. Diffraction, on the other hand, is the bending and spreading of light waves as they pass through a narrow slit. In the context of single slit patterns, interference occurs when the diffracted waves interfere with each other, leading to the observed pattern.
4. Can single slit interference and diffraction occur with other types of waves, such as water waves or sound waves?
Ans. Yes, single slit interference and diffraction can occur with other types of waves as well, not just light waves. Water waves, sound waves, and even electron waves can exhibit similar interference and diffraction patterns when passing through a narrow slit. The principles behind the phenomenon remain the same, regardless of the type of wave.
5. How can the interference and diffraction pattern be used in practical applications?
Ans. The interference and diffraction pattern produced by a single slit have various practical applications. For example, they are utilized in spectrometers to analyze the composition of light by separating it into its constituent wavelengths. They are also important in the design of optical devices such as cameras and telescopes, where they help in improving image quality and resolving power. Additionally, the interference and diffraction patterns are fundamental in understanding wave behavior and studying the properties of different materials.
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