• All electromagnetic radiation is created in the same way, by accelerating electrical charge.
• Know the electromagnetic spectrum, and the relative positions of the various types of radiation

• All radiation is produced in the same way, by accelerating electrical charges.
• By analyzing the electromagnetic equations, Maxwell realized that there were more types of radiation than just visible light. He predicted the entire spectrum.
• This was a test of his theory, and was verified by Hertz in the late 1880’s when he discovered radio waves.
• The entire electromagnetic spectrum is a continuum of waves that can be thought of in terms of frequencies, wavelengths, or energy; it does not matter which.
• The gross properties of different types of radiation can be understood in terms of the differences between their respective wavelengths, or between their respective energies. It does not really matter which way you look at it.
• Units of length:
mm = micron = 1/1000 mm
nm = nanometers = 10^-9 m = 1/1000 mm
Å = angstroms = 10^-10 m = 0.1 nm = 1/10,000 mm

• Oscillating electrons along a tall metal antenna produces the waves.
• The speed of oscillation determines the wavelength
• AM and FM transmissions:
Broadcaster is limited to a very narrow bandwidth.
AM = amplitude modulated, long l, eg 670 kHz (kilo = 10³). Since the radio waves are long they can scatter off the layers of the atmosphere.
FM = frequency modulated, short l, eg 92.1 MHz (Mega = 10⁶). Since these radio waves are shorter than AM waves they can also carry more energy and are able to penetrate objects more easily. Therefore FM radio signals can be recieved indoors more easily. However, they also penetrate the atmosphere easily too, so FM radio signals are not recieved far from their transmitting source.
TV is a mix of both, AM for sound, FM for picture

• Satellite radio works at around 2.3 GHz (Giga = 10⁹), a frequency that has more energy than FM.

• The short wavelength of microwave beams means that it is easy to make a beam that is narrow and well-defined in its size.
• Microwave transmitters, TV, satellite, phone
• Radar, and stealth fighters. Modern military radar can detect a fly at a distance of 1 mile. Stealth fighters use paints that absorb microwave, and are constructed with weird angles to reflect the signal in strange ways.
• Microwave ovens oscillate H₂O molecules.

• Radiation from heat is in this range.
• Our skin is a crude infrared detector
• Energy leaks in homes
• Guidance of air-to-air missiles

• The range of electromagnetic radiation that our eyes can see.
• We do not see all wavelengths with the same sensitivity.

• Energy is now high enough to break many chemical bonds.
• This is why we can be sunburned.
• Used to clean things, e.g. hospital equipment
• Black lights – cause fluorescence

• Wavelength short enough to penetrate most forms of matter.
• That is why it is used to examine broken bones.
• Crystallography
• High energy is deadly

• Down to the size of the nucleus
• Astronomy uses gamma rays because they must have been given off by high energy events

• uses the whole radio energy spectrum
• messages are sent from a transmitter to a reciever at a set of predetermined wavelengths known only by these two devices
• Signals are binary, ie 0 or 1. They are sent millions of a time per second with a 0 being 10 picoseconds (10 trillionths of a second) early, and a 1 being 10 picoseconds late.
• Exciting properties of the devices are that they are secure, small, little power needed, can provide positional information, high-capacity, can work through the earth, "sees" through objects.
• Commonly known as "impulse" or "ultra-wide band" (UWB) radio or radar
• Time Domain (http://timedomain.com)
• Problems include the FCC because licensing frequencies is a billion dollar industry. Eg a FM station sold for $110 million in LA recently. FCC finally granted them a license in 2002.