Shortcut Methods

Shortcut Methods and Tricks to Solve Numerical Problems on Interference of Light


Double-Slit Interference

  • Fringe width: β=λDd, where (\beta) is the fringe width, (\lambda) is the wavelength of light, (D) is the distance from the slits to the screen, and (d) is the slit separation.
  • Separation of bright fringes: Δx=λDd
  • Intensity distribution: I=I0cos2(πdλDx), where (I_0) is the maximum intensity and (x) is the distance from the central fringe.

Michelson Interferometer

  • Wavelength of light λ=2DN, where (D) is the path difference and (N) is the number of fringes observed.
  • Coherence Length lc=λ2(Δλ), where (l_c) is the coherence length and (\Delta \lambda) is the spectral bandwidth of the light source.

Young’s Double-Slit Experiment

  • Fringe spacing x=λDd, where (x) is the fringe spacing, (\lambda) is the wavelength of light, (D) is the distance to the screen, and (d) is the slit separation.
  • Fringe width β=2λDd, where (\beta) is the fringe width.
  • Total Number of fringes: N=Dβ=d2λ

Coherence and Incoherence

  • Coherent sources: Emit waves with the same frequency, constant phase difference, and a definite phase relation.
  • Incoherent sources: Emit waves with random phase differences and no definite phase relation.

Thin Film Interference

  • Condition for constructive interference: 2tn=mλ,m=0,1,2,3,
  • Condition for destructive interference: 2tn=(m+12)λ,m=0,1,2,3, where (t) is the film thickness, (n) is the refractive index of the film, (\lambda) is the wavelength of light, and (m) is the order of interference.