Electromagnetic Radiation
Electromagnetic radiation is energy, such as that produced by the Sun, that can travel through empty
space as transverse waves. All the different types of electromagnetic radiation together are often
called the electromagnetic spectrum.
The Electromagnetic Spectrum
The electromagnetic spectrum is a collection of all electromagnetic waves arranged in order
according to wavelength. This spectrum includes not only visible light (which makes up only a small
portion of this spectrum) but also microwaves, ultraviolet light, infrared light, radio waves, and
gamma waves. The wavelength is the distance between two successive crests or troughs in the
wave.
The diagram above shows the basic organization of the electromagnetic spectrum. The spectrum of
waves can be divided into sections based on wavelength. The shortest waves are gamma rays, which
carry the most energy and have wavelengths of 1 x 10-12 meters or less. The longest waves are radio
waves, which carry the least energy and can have wavelengths of many kilometers.
The Sun Produces Electromagnetic Waves
Powerful nuclear reactions take place within the Sun. As these reactions release an enormous
amount of energy in the form of electromagnetic radiation, the Sun is constantly losing energy. Some
of the electromagnetic energy is commonly called light. Sometimes the wide spectrum of colors of
light that the Sun emits is referred to as white light.
Only a tiny fraction of the electromagnetic radiation that the Sun emits actually reaches the Earth. The
Sun is very large compared to the Earth, and it is very far away. Radiation travels out from the Sun in
every direction, in the shape of a giant sphere. Because the Earth is so small and so far away, only a
very small portion of this expanding sphere of energy collides with it.
The Earth receives only a tiny fraction of the electromagnetic radiation produced by the Sun.
All electromagnetic energy from the Sun passes through the vacuum of space at the speed of light
(300 million meters per second) in the form of transverse waves. Some types of electromagnetic
radiation that are important to humans are discussed below:
•
Visible light is a particular band of electromagnetic radiation that can be seen and sensed by the
human eye. This energy consists of the narrow portion of the spectrum with wavelengths from 0.4
micrometers (violet) to 0.7 micrometers (red).
Water droplets in the air can bend the component wavelengths of white light different amounts so
that each color becomes visible. This phenomenon is known as a rainbow.
•
Ultraviolet radiation is another form of energy that comes from the Sun. Ultraviolet rays are higher
in energy than waves of visible light. Ultraviolet rays are not detectable by the human eye. Most
people have felt the effects of these rays, however, in the form of a sunburn. Sunburns occur
because even though we cannot see ultraviolet rays, they can still damage a person's skin if the
person stays out in the sun for too long. Sunburns cause skin to become red and irritated. It is
possible to prevent sunburn through the use of sunblock. Some types of sunblock work by absorbing
UV radiation before it can reach the skin. Another type—a thick, white ointment—works by reflecting
the radiation.
Image obtained from NOAA NWS.
Exposure to ultraviolet rays from the Sun can cause skin damage called sunburn.
•
Infrared radiation is produced by the motion of the atoms and molecules that make up everything in
the universe. The faster the atoms and molecules are moving, the more infrared radiation they
produce. This movement also produces heat, which humans can feel when they get near an object.
In general, the warmer an object is, the more infrared light it emits.
Infrared light has wavelengths that are slightly longer than visible light, so they are lower in energy
than visible light waves, and they cannot be seen by the human eye. However, infrared radiation can
sometimes be detected by nerves in the skin. For example, radiators and other types of heaters
produce infrared radiation. It is possible to feel the warmth coming off of the heaters. The infrared
range starts at the end of the red spectrum with wavelengths greater than 0.7 micrometers.
The cat sitting in front of the radiator can feel the infrared radiation given off by the radiator, even
though the radiation is not visible.
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