The Electromagnetic Spectrum

Electric Field

Magnetic Field

v

Electromagnetic Radiation (EMR) is a special type of wave consisting of oscillating electric and magnetic fields.  Unlike other wave types it can occur and travel through a vacuum.  It may be said that the medium in this case is not physical matter.  Rather the medium consists of the electric and magnetic fields that undergo disturbance or fluctuation.  The disturbance propagates due to the fact that a changing electric field produces a magnetic field and a changing magnetic field produces a changing electric field.  The two fields therefore oscillate back and forth as illustrated in the diagram below.

Notes:

• The electric and magnetic fields and the velocity are mutually perpendicular vectors.
• The plane of the electric oscillations is perpendicular to the plane of the magnetic oscillations.  The velocity is along the line where the two planes intersect.
• This pattern of disturbance travels at a speed:  c = 299792458 m/s
• A very wide range of frequencies and wavelengths are possible.  Depending on the value of frequency and wavelength scientists categorize the EMR as radio, microwave, infrared, visible light, ultraviolet, x-ray, and gamma.  

The following chart shows examples of the different types of EMR.  Use your calculator to determine the missing values and complete the table.

	Example	Frequency	Wavelength
Radio	AM station (WNOX)	990 kHz
	FM station (WIMZ)	103.5 MHz
	TV station (VHF ch 10)	195 MHz
	TV station (UHF ch 43)	647 MHz
Microwave	microwave oven	2450 MHz
	classroom generator	10.525 GHz
Infrared	human being (98.6 °F)		9.35 μm
	hot oven (300 °F)		6.87 μm
	remote control		940 nm
Visible Light	far red		750 nm
	red laser pointer		650 nm
	green laser pointer		532 nm
	deep violet		400 nm
Ultraviolet	UVA		365 nm
	UVC		100 nm
X-ray	“soft”		1 nm
	“hard” (medical)		2.48 × 10^-11 m
Gamma	radioactive cobalt-60		9.31 × 10^-13 m

• The above information represents the wave model of EMR.  A different way to understand EMR is to use the particle model.
• In the particle model of EMR the above phenomena are said to exist in the form of photons.  A photon is a discrete “particle” of EMR energy – also sometimes thought of as a “wave packet”.  In this view, a beam of light is not a continuous wave but rather more like a stream of many individual “wave bullets”. 
• Experiments show that the amount of energy contained in a single photon is directly proportional to its frequency (E = hf, h = Planck’s constant).  Therefore the table above shows the different types of EMR in order of increasing energy per photon.
• Both the wave model and the particle model can be experimentally demonstrated – therefore scientists say that light and EMR exhibit wave-particle duality.