Refraction of light part 2
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Refraction of Light –Part 2. Internal Reflection. When light travels from a slow medium to a fast medium, the angle of refraction is larger than the angle of incidence. When the angle of refraction should be 90 o or greater, there is total internal reflection.

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Internal reflection
Internal Reflection

  • When light travels from a slow medium to a fast medium, the angle of refraction is larger than the angle of incidence.

  • When the angle of refraction should be 90o or greater, there is total internal reflection.

  • The incident angle which predicts a 90o refraction angle is called the critical angle.

  • Applet


Critical angle
Critical Angle

  • n1sin qc = n2 sin 90o

  • n1sin qc = n2

  • sin qc = n2 / n1

  • qc = sin-1(n2 / n1)

  • For water: qc = 48o

  • The higher the index of refraction the lower qc





Internal reflection1
Internal Reflection

  • All rays reflect internally, but the top three rays reflect only a small percentage internally; most energy leaves the prism.

  • The fourth and fifth rays are reflected 100 % internally



Internal reflection in diamond
Internal Reflection in Diamond

  • The critical angle fordiamond in air is24.5 o.

  • Any ray which strikes the inside surface at an angle greater than 24.5o will be totally internally reflected.




Dispersion blue bends best
DispersionBlue Bends Best


Different frequencies different indices of refraction
Different FrequenciesDifferent Indices of Refraction


Refractive index function of wavelength
Refractive IndexFunction of Wavelength




Rainbow formation
Rainbow Formation

  • An observer seesred light comingfrom droplets ofwater higher inthe sky.

  • Droplets of waterlower in the skysend violet lightto the eye.










Alexander s dark band
Alexander’s Dark Band

  • Sky is light inside primary rainbow

  • Dark between primary and secondary bows

  • Light beyond the secondary rainbow

  • Dark region between is called Alexander’s Dark Band


22 o halo
22o Halo

  • A halo is a ring of light surrounding the sun or moon.

  • Most halos appear as bright white rings but in some instances, the dispersion of light as it passes through ice crystals found in upper level cirrus clouds can cause a halo to have color.

Diameter less than 20.5 micrometers

Randomly oriented hexagonal ice crystals


Sundogs
Sundogs

  • Sundogs or parhelia on right and left of sun

Flat faces horizontally oriented

Hexagonal ice crystals

Diameter greater than 30 micrometers





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