Wave Optics


  • Diffraction Confirms wave nature of Light
  • The Light waves are diffracted only when the size of the obstacle is comparable to the wave length of Light.
  • Condition for observing diffraction.
    \tt l\approx\frac{b^{2}}{4\lambda}
    l = distance between screen and object
    b = size of object
  • In Fresnels diffraction sources and screen are at finite distance
  • No Lenses are required in fresnels diffraction.
  • The incident wave fronts in Fresnels diffraction are either spherical (or) cylindrical.
  • In Fraunhoffer diffraction source and screen are at infinite distance
  • Lenses are required to observe the fraunhoffer diffraction.
  • The incident wave fronts in Fraunhoffer diffraction are plane wave fronts.
  • Fraunhoffer diffraction is limiting case of fresnels diffraction.
  • Condition for minimum intensity in fraunchoffer a sin θ = nλ {n = 1, 2, 3 …….} (a = width of slit)
  • Condition for miximum intensity in fraunchoffer \tt a \sin\theta=\left(2n+1\right)\frac{\lambda}{2} {n = 1, 2, 3 …….} (a = width of slit)
  • Width of central maxima\tt \beta_{0}=\frac{2D\lambda}{a}=\frac{2f\lambda}{a}

View the Topic in this video From 00:18 To 8:11

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Diffraction of a single slit:
1. For minima d sin θ = nλ, where n = 1, 2, 3 .....
2. For maxima d sin θ = (2n + 1)\frac{\lambda}{2}, where n = 1, 2, 3 ....