Lesson One : The Electromagnetic Spectrum
The electromagnetic spectrum consists of all the possible wavelengths of electromagnetic radiation, extending from high energy, short wavelength radiation to low energy, long wavelength radiation. Scientists have given names to different ranges of the spectrum to aid identification, but the fundamental organization of the spectrum is from high energy to low energy.Gamma rays are the most energetic form of electromagnetic radiation. Gamma rays have wavelengths of less than one hundred trillionths of a meter (1 × 10-14 m). Gamma rays – produced by many radioactive elements – are so energetic that they damage living organisms.
X-rays have wavelengths between one trillionth of a meter (1 × 10-12 m) and 10 billionths of a meter (1 × 10-10 m). X-rays are used primarily for medical purposes, though they must be used with caution since they are energetic enough to destroy living cells.
Ultraviolet (UV) radiation (which literally means "above violet") has a wavelength between 400 billionths of a meter (4 × 10-11 m) and 6 ten-billionths of a meter (6 × 10-10 m). The sun is the most prominent source of UV radiation and it is this radiation that causes sunburn when skin is exposed to sunlight for extended periods of time.
The electromagnetic spectrum consists of all the possible wavelengths of radiation. The visible spectrum, the narrow range of wavelengths which human eyes can perceive as the colors of the rainbow, is only a small part of the electromagnetic spectrum.
Infrared (IR) radiation, which literally means "below red", ranges from 700 billionths of a meter (7 × 10-11 m) on up to 1 millimeter (1 mm). IR radiation, which is more commonly known as heat, is produced by a variety of objects and is used in many areas including physical therapy, IR photography, night vision, and IR astronomy.
Microwaves have wavelengths ranging from one ten thousandths of a meter (1 × 10-4 m) up to around one tenth of a meter (0.1 m). They are generated by electronic devices and are often used in radar systems, although their most familiar application is in microwave ovens.
Radio waves, last and certainly least in terms of energy, have a wavelength greater than one tenth of a meter (0.1 m). Radio waves are generated by current flowing in conductors and are regularly used in radio receivers, television communications, and, most importantly for our purposes, radio astronomy.
It is important to note that radio waves are not sound waves. The device located in the dashboard of your car, colloquially referred to as a "radio", is actually a radio receiver. It receives signals from a transmitter in the form of electromagnetic radio waves and translates those waves into the sound waves that are emitted from the car's speakers.