What is the diffreence between Frensel’s diffraction and Fraunhofer diffraction ?,,What happens to the Fraunhofer diffraction of light, when it is placed in water?,, Colored spectrum is seen when we see through muslin cloth. Why?

What is the diffreence between Frensel’s diffraction and  Fraunhofer diffraction ?
 
Ans: During diffraction, If the source of light and screen are at finite distance from the obstacle, then it is called Frensel diffraction whereas if the source of light and screen are kept at infinite distance from the aperture or obstacle, it is called Fraunhofer’s diffraction.
Light does not need to be converged in Frensel’s diffraction. So, no lens is used to converge the beam light. But, lenses and mirrors are used to converge and modification of diffracted light in Fraunhofer’s diffraction.

. What happens to the Fraunhofer diffraction of light, when it is placed in water?
Ans: The wavelength and decreases is less in water than in air. So, wavelength of light is less in water than in air. In diffraction, the width of central maximum has direct relation to the wavelength of the light used i.e., β∝ λ. So, when the apparatus is placed in water, the width of central bright maximum decreases.
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 Colored spectrum is seen when we see through muslin cloth. Why?
Ans: Muslin cloth is made up of very fine thread which acts like thin slits. When white light is passed through this cloth, the light get diffracted and interference of these diffracted beams give rise to a colored spectrum.