Electromagnetic spectrum charts the continuous spread of all types of electromagnetic waves . Such waves are forms of energy . Light consists of electromagnetic waves. The colors of the rainbow form a spectrum of visible light. The full electromagnetic spectrum also includes forms of energy that cannot be seen by the human eye. These invisible electromagnetic waves include radio waves and X rays.
Frequency and wavelength.
Electromagnetic waves are the oscillations (back-and-forth movements) of electric and magnetic fields. The electromagnetic spectrum charts the frequency and wavelength of these oscillations. Frequency is the number of oscillations that an electromagnetic wave makes per second. It is measured in units of hertz (Hz), where one Hz is one oscillation cycle per second. Wavelength is the length of one cycle, measured in meters (m).
The relationship between frequency and wavelength can be calculated using the formula:
frequency x wavelength = speed of light.
Since the speed of light is constant (299,792,458 meters per second), the formula shows that frequency and wavelength are inversely related. Higher frequencies correspond to smaller wavelengths and lower frequencies correspond to larger wavelengths.
Light visible to the human eye makes up a very small part of the entire electromagnetic spectrum, from around 4×10-7 meters (violet) to 7×10-7 meters (red) in wavelength. Some animals can detect parts of the spectrum that are not visible to humans.
In order from highest to lowest frequency, the types or electromagnetic waves are: gamma rays , X rays , ultraviolet , visible light, infrared , microwaves , and radio waves . Microwaves are typically classed as a kind of radio wave. Radio waves have the longest wavelength and lowest energy. Gamma rays have the shortest wavelength and the highest energy.
Unlike ocean waves, which seem continuous in their up-and-down motion, electromagnetic waves take the form of quanta—units or “chunks” of energy. The quantum unit of the electromagnetic field is called the photon . Photons have properties of particles as well as waves. The energy of a photon is proportional to the frequency of the corresponding electromagnetic wave.
Uses and study.
Different parts of the electromagnetic spectrum have many applications in science and technology. Doctors use X rays to image bones and other structures beneath human skin. Microwaves are used to heat food. Radio waves encode many kinds of communication signals. Remote control devices emit infrared light that can be detected by electrical devices in cars and such home entertainment equipment as television sets and DVD players.
Electric current in a variety of devices can produce electromagnetic waves and detect their reflections. Such devices include radar, remote sensing devices for mapping Earth and other planetary surfaces, metal detectors for locating lost items, and airport and store security detectors.
Beyond practical uses, the electromagnetic spectrum provides scientists a means to understand the composition of the universe and the nature of space and time. The cosmic microwave background , or CMB, is a “bath” of microwave energy that exists everywhere in space. Scientists believe it is left over from the earliest, explosive moments of the universe.
The electromagnetic spectrum may not be infinite (without limits). Scientists now speculate that the shortest possible wavelength might be around 1.6×10-35 meters, known as Planck Length. The longest possible wavelength may be the size of the universe itself.
