5.1. Light http://www.ck12.org
Visible light is one type ofelectromagnetic radiation,which is a form of energy that exhibits wavelike behavior
as it moves through space.Other types of electromagnetic radiation include gamma rays, x-rays, ultraviolet light,
infrared light, microwaves, and radio waves. Pictured below (Figure5.1) is theelectromagnetic spectrum,which
includes all forms of electromagnetic radiation.Notice that visible light makes up only a very, very small portion
of the entire electromagnetic spectrum. All electromagnetic radiation moves through a vacuum at a constant speed
of 2.998× 108 m/s. While the presence of air molecules slows the speed of light by a very small amount, it is still
equal to 3.00× 108 m/s when rounded to three significant figures, so this is the value that we will use.
FIGURE 5.1
The electromagnetic spectrum encompasses a very wide range of wave-
lengths and frequencies. Visible light is only a very small portion of the
spectrum, with wavelengths from 400-700 nm.You can tour the electromagnetic spectrum at http://missionscience.nasa.gov/ems/index.html.
Waves are characterized by their repetitive motion. Imagine a toy boat riding the waves in a wave pool. As the
water wave passes under the boat, it moves up and down in a regular and repeated fashion. While the wave travels
horizontally, the boat only travels vertically up and down. Below are two examples of waves (Figure5.2).
FIGURE 5.2
(A) A wave consists of an alternation be-
tween crests and troughs. The wave-
length is defined as the distance between
any two consecutive identical points on
the waveform. The amplitude is the height
of the wave. (B) A wave with a short
wavelength (top) has a high frequency
because more waves pass a given point
in a certain amount of time. A wave with
a longer wavelength (bottom) has a lower
frequency.A wave cycle consists of one complete wave—starting at the zero point, going up to a wave crest, going back down
to a wave trough, and back to the zero point again. Thewavelengthof a wave is the distance between any two
corresponding points on adjacent waves. It is easiest to visualize the wavelength of a wave as the distance from
one wave crest to the next. In an equation, wavelength is represented by the Greek letter lambda (λ). Depending