PS-7.5   Summarize the characteristics of the electromagnetic spectrum (including range of wavelengths, frequency, energy, and propagation without a medium).
Key Concepts
Electromagnetic spectrum
Visible spectrum
Propagation without a medium
The electromagnetic spectrum includes of all forms electromagnetic energy. The only difference between any one form of electromagnetic energy and the next, is the wavelength, and therefore the frequency, of the wave. 
All forms of electromagnetic energy move through a vacuum at the speed of light, 2.99 x 108m/s or 186000mi/s. This is REALLY fast! At this speed it only takes light 1second to go from the moon to the Earth...and only 8min. for light to reach us from the Sun.
Unlike sound waves, electromagnetic energy waves can move through a vacuum. This is why light waves and other forms of electromagnetic energy can travel through space. As a matter of fact, electromagnetic energy waves travel fastest through the vacuun of outer space than they do through air or other transparent materials. Unlike sound waves and other mechanical waves, electromagnetic energy waves DO NOT need a medium to travel through.

The electromagnetic spectrum consists of a wide range of wavelengths and frequencies. The longest wavelengths are the radio waves and the shortest wavelengths are the Gamma rays. Remember there is an inverse relationship between wavelength and frequency. The long wavelengths are the lowest frequencies and the shorter wavelengths are the higher frequencies. This is one reason Gamma rays damage living organisms, and why ultra violet light can burn your skin...higher frequencies carry more energy, and high energy waves damage living cells! Remember: Wave energy is directly proportional to wave frequency. Here is a graph of wave energy vs. wave frequency.
***Students: You should know the order of electromagnetic waves from low frequency to high
radio waves, microwaves, infrared radiation,  (red, orange, yellow,green, blue, Indigo, violet), ultraviolet, X-rays, and gamma rays.
                        
Low Frequency_________________________________________________High Frequency