Wavelike Properties of Electromagnetic Radiation
1. Wave parameters
2. Refractiona. Index of refraction
Snell’s Law
b. Prism monochrometers
3. Diffraction
a. slit width
4. Reflection
5. Scattering
Wave parameters
Wavelength depends upon the medium the electromagnetic radiation is traveling in
Frequency is a set quantity dependent on radiation source
c = only strictly true in a vacuum
Refraction: deflection of propagating waves at boundary
between 2 media of 2 different refractive indexes
• As light moves from high velocity medium to low velocity medium, light moves toward normal
• A beam of light at a wavelength of 550nm in air is incident on a slab of transparent material. It has an angle of incidence of 40o with the normal and the refracted beam makes an angle of 26o with the normal. Find n for the material. What is the wavelength of light in the material?
Refraction is most common way wavelike properties of light manifest themselves
Instruments benefit from this in:
monochrometer design
What is a monochrometer?
Something which selects for just one wavelength of light.
Reflection
• Calculate what the % transmittance of light going perpendicular through regular plate glass (n = 1.50) will be.
Ways to reduce reflected losses
• 1) Coating with a low reflectance material
• 2) Cementing optical elements that are in contact with a material of similar refractive index (rather than leaving air gaps in between).
• Reflectance as a function of angle of incidence
Scattering
Particles will scatter light if:Particles will scatter light if:1) The particles have 1) The particles have
dimensions on the order of dimensions on the order of magnitude or smaller than incident magnitude or smaller than incident wavelengthswavelengths
2) Are randomly distributed in 2) Are randomly distributed in a medium of refractive index a medium of refractive index different than their owndifferent than their own
Structures Producing Scattering
Wavelength (m)
Spectral Region
Max. Particle Size (m)
Type of Aggregate
10 IR 15 Large colloidal particles
0.5 Visible 0.75 Colloidal particles, macromolecules
0.001 X ray 0.002 Small molecules, atoms
A Chemical Sunset Demo
1. How is this reaction similar to a natural sunset?
2. What causes the different colors to be produced?
3. What other compounds might produce a similar reaction?
4. What is a colloidal suspension?
A Chemical Sunset Demo
What color light will be scattered the most?
Why is the sky blue?
Some forms of spectroscopy rely upon scattering like Raman spectroscopy
Why should you not touch cuvettes?
