Understanding Frequency, Wavelength, and Intensity in Physics

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Frequency (f) = 1/Time (t)

Wave Speed (v) = f * Wavelength (λ)

Fobserver = (fsource * speed of sound (v)) / (v ± vsource)

Λobserver = (v ± vsource) / d

Intensity (W m-2) = Power / Cross Sectional Area

Intensity (I) = 1 / Amplitude2

Electromagnetic waves travel at the same speed of 3.0*108 m/s in a vacuum, but have different wavelength and frequencies

The regions of the electromagnetic spectrum in order of increasing wavelength are:

  • γ-rays
  • x-rays
  • ultraviolet
  • visible
  • infrared
  • microwaves
  • radio waves

Understanding Fringes and Interference in Young's Double Slit Experiment

A monochromatic light source is placed behind a single slit to create a small, well-defined source of light. Light from this source is diffracted at the slit producing 2 lit sources at the double slit S1 and S2. These 2 light sources are coherent and they create sustained and observable fringes as shown in the figure. Bright fringes are seen when constructive interference occurs, that is when the path difference between the 2 diffracted waves from sources S1 and S2 is nλ. Dark fringes are seen when destructive interference occurs. The condition for a dark fringe is that the path difference should be (n + 1/2)λ. The distance between successive bright fringes is called fringe width (Young's Double Slit).

λ = ax / D

a = slit separation, the distance between the center of slits

x = fringe separation, the distance between the centers of adjacent bright/dark fringes

d = slit to screen distance, distance from the midpoint of slits to the central fringe on the screen

d sin θ = nλ or sin θ = nλ / d

d = distance between adjacent lines of grating

n = order of maximum

θ = λ / d (only if θ is <5)

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