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Light Scattering

Light Scattering

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Light Scattering

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  1. LightScattering A Classical electrodynamics view.

  2. Introduction • Light scattering is the dispersal of light in different directions away from the source beam. • There are different kinds of scattered light based on their range of frequency. • The sky is blue, clouds are white and the sunset is red all due to light scattering. • Light scattering can be explained using theories of classical electrodynamics and statistical mechanics.

  3. Light has both magnetic and electronic fields. As light travels from the sun, its electric field interacts with molecules in the air to form dipoles. The strength of the dipole depends on two factors, Light intensity Molecule polarizability Light is a wave and therefore causes the dipole to oscillate Light Scattering: A Classical Electrodynamics View.

  4. A dipole can oscillate at three frequencies, ω, ω-ωv and ω+ωv These terms correspond to Rayleigh scattering, Stokes Raman scattering and anti-Stokes Raman scattering respectively. The intensity of the emitted light is, I = ω4μo2 3C3 The intensity of the scattered light is proportional to the fourth power of the frequency and is the reason why the sky is blue.

  5. Mathematical Representation µ=aE E(t)=E0aCost a(t)= a0+ a1Cos vt

  6. The Blue Sky • Blue light has the shortest wavelength in the visible spectrum and therefore has the most intensity of the scattered light rays. • We see the blue skys when we look away from the sun because this is where most of the scattered light is.

  7. Blue Sky • Reference: Carl R Nave Department of Physics and astronomy Georgia State University. Rayleigh Scattering (2004) http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html Acquired Monday 7th December 2004.

  8. Sunsets • At dusk and dawn, the sun rays have to travel a greater length through the atmosphere. • Most of the blue light is scattered in other directions thus when we look at the sun in the horizon it appears red.

  9. White Clouds. • Clouds are mainly composed of water droplets which are much larger than the wavelength of light • Due to this property, the water droplets scatter all the light at high intensity thus clouds appear white.