Superposition of Waves

Superposition of Waves

1. Diffraction

   • Diffraction is the spreading of waves through an aperture or round an obstacle.
     • It is observable when the width of the aperture is of the same order of magnitude as the wavelength of the waves
   • Conditions for Diffraction
     • The size of the aperture of obstacle is small enough.
     • The wavelength is large enough.
   • Frequency, wavelength and speed don't change. Only direction of propagation does.
   • Diffraction Grating
     • A diffraction grating is a plate on which there is a very large number of parallel, identical, very closely spaced slits.
       • The bright fringes also known as maxima caused by constructive interference
         • The dark fringes are caused by destructive interference
           • ? sin ? = ?λ
             • d: distance of adjacent grating lines
             • ?: angle of diffraction
             • ?: order of diffraction
           • X = Dλ/n
             • X: bond width
             • D: distance between sources & screen
             • n: distance between 2 sources
     • Condition
       • Width of the slit should be fraction of a mm
       • The 2 sources should be 1 mm apart
       • Distance from source to screen should be 1 meter
       • Sources should be coherent

2. Interference

   • Destructive Interference
     • Waves out of phase produce a shallower wave
   • Condition for Interference
     • Light source must be coherent
     • Same wavelength
     • Frequency doesn't change for coherent sources
   • Constructive Interference
     • Waves in the same phase produce higher crest and deeper troughs
   • interference refers to what happens when two waves overlap

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