3.3 Electromagnetic (EM) Waves  
  3.3.2 EM Spectrum Chart  
One of the most important diagrams in both science and engineering is the chart of the EM spectrum which is illustrated in Figure . The typical EM spectrum diagram summarizes the ranges of frequencies, or bands that are important to understanding many things in nature and technology. EM waves can be classified according to their frequency in Hz or their wavelength in meters. The EM spectrum has eight major sections, which are presented in order of increasing frequency and energy, and decreasing wavelength:
  1. Power waves - These are the slowest of all EM radiation and therefore also have the lowest energy and the longest wavelength.
  2. Radio waves - This is the same kind of energy that radio stations emit into the air for a radio to capture and play. However, other things such as stars and gases in space also emit radio waves. Many communication functions use radio waves.
  3. Microwaves - Microwaves will cook popcorn in just a few minutes. In space, astronomers use microwaves to learn about the structure of nearby galaxies.
  4. Infrared (IR) light - Infrared is often thought of as being the same thing as heat, because it makes our skin feel warm. In space, IR light maps the dust between stars.
  5. Visible light - This is the range that is visible to the human eye. Visible radiation is emitted by everything from fireflies to light bulbs to stars. It is also emitted by fast-moving particles hitting other particles.
  6. Ultra-violet (UV) light - It is well known that the sun is a source of ultraviolet (UV) radiation. It is the UV rays that cause our skin to burn. Stars and other hot objects in space emit UV radiation.
  7. X-rays - A doctor uses X-rays to look at bones and a dentist uses them to look at teeth. Hot gases in the universe also emit X-rays.
  8. Gamma rays - Natural and man-made radioactive materials can emit gamma rays. Big particle accelerators that scientists use to help them understand what matter is made of can sometimes generate gamma rays. However, the biggest gamma-ray generator of all is the universe, which makes gamma radiation in many ways.

The most important range for this course is the RF spectrum. The RF spectrum includes several frequency bands including microwave and the Ultra High Frequencies (UHF) and Very High Frequencies (VHF) bands of terrestrial radio and television broadcasting. This is also where WLANs operate. The RF spectrum ranges from nine kHz to thousands of GHz. It actually consists of two major sections of the EM spectrum, radio waves and microwaves. For historical reasons, many people refer to both sections together as the RF spectrum. The RF frequencies, which cover a significant portion of the EM radiation spectrum, are used heavily for communications.

Most of the RF ranges are licensed, though a few key ranges are unlicensed.

   
 

Interactive Activity

Interactive Activity: Electromagnetic Spectrum

This activity allows the student to scroll through the EM spectrum by moving the mouse to the left or right over the graphic.