Light as a wave phenomenon

Recall that waves can be categorized into two major divisions:

Mechanical waves, which require a medium. These include sound, water and waves on a (guitar, etc.) string

Electromagnetic waves, which travel best where there is NO medium (vacuum), though they can typically travel through a medium as well. All electromagnetic waves can be represented on a chart, usually going from low frequency (radio waves) to high frequency (gamma rays). This translates to: long wavelength to short wavelength.

All of these EM waves travel at the same speed in a vacuum: the speed of light (c).

The standard wave velocity equation is still:




But for light, where c is the speed of light (3 x 10^8 m/s ):

c = f l


Still, f is frequency (in Hz) and l is wavelength (in m).

(We will see during the next class that the speed of light, while constant in a vacuum, is NOT constant in other mediums.  That is, the speed of light does depend on what it travels through - and this causes refraction to occur, usually exhibited by bending of light.  More to come!)


General breakdown of e/m waves from low frequency (and long wavelength) to high frequency (and short wavelength):

Radio
Microwave
IR (infrared)
Visible (ROYGBV)
UV (ultraviolet)
X-rays
Gamma rays

In detail, particularly the last image:

http://hyperphysics.phy-astr.gsu.edu/hbase/ems1.html


http://www.unihedron.com/projects/spectrum/downloads/full_spectrum.jpg

Don't forget - electromagnetic waves should be distinguished from mechanical waves (sound, water, earthquakes, strings on a guitar/piano/etc.). 

ALL E/M waves (in a vacuum) travel at the SPEED OF LIGHT (c).




For E/M waves, the speed is the speed of light, so the expression becomes:

c = f  l

Note that for a given medium (constant speed), as the frequency increases, the wavelength decreases.





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