Figure 20.17: Light from objects at different distances is focused by the lens of the eye;
muscles in the eye control the shape of the lens so the light is focused on the back of the eye
no matter how far the object is from the lens. ( 17 )
The Nature of Light
Visible lightis a type of electromagnetic (EM) radiation. It’s the only type of EM radiation
that can be detected by the human eye. To be visible to humans, EM radiation has to travel
in waves of certain wavelengths. Wavelength is the distance from any point on one wave to
the same point on the next wave. The different types of electromagnetic radiation are shown
inFigure20.18. Just a small part of the full range of EM radiation is visible to the human
eye.
Electromagnetic RadiationFigure 20.18: This diagram shows the wavelengths of electromagnetic radiation, from short-
est (extreme left) to longest (extreme right); the human eye can detect only visible light,
which falls in a narrow range of wavelengths, but the eyes of some animals can detect radi-
ation of different wavelengths; bees can see ultraviolet radiation. ( 16 )