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FIGURE 7.18 The flowers appear to be red because they reflect light in the 7.9 × 10 m to 6.2 × 10 m range of wavelengths.
speed of electromagnetic waves (c) is related to the wavelength a local fair and bought several triangular glass prisms. He then pro-
(λ) and the frequency (f ) by ceeded to conduct a series of experiments with a beam of sunlight
in his room. In 1672, he reported the results of his experiments
c = λf
with prisms and color, concluding that white light is a mixture of
equation 7.3 all the independent colors. Newton found that a beam of sunlight
falling on a glass prism in a darkened room produced a band of
Visible light is the part of the electromagnetic spectrum
that your eyes can detect, a narrow range of wavelength from colors he called a spectrum. Further, he found that a second glass
prism would not subdivide each separate color but would com-
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about 7.90 × 10 m to 3.90 × 10 m. In general, this range of bine all the colors back into white sunlight. Newton concluded
visible light can be subdivided into ranges of wavelengths that that sunlight consists of a mixture of the six colors.

you perceive as colors (Figure 7.18). These are the colors of the
rainbow, and there are six distinct colors that blend one into

another. These colors are red, orange, yellow, green, blue, and vio- EXAMPLE 7.2
let. The corresponding ranges of wavelengths and frequencies of

these colors are given in Table 7.2. The colors of the spectrum can be measured in units of wavelength,
In general, light is interpreted to be white if it has the same frequency, or energy, which are alternative ways of describing colors of

mixture of colors as the solar spectrum. That sunlight is made up of light waves. The human eye is most sensitive to light with a wavelength
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of 5.60 × 10 m, which is a yellow-green color. What is the frequency
component colors was first investigated in detail by Isaac Newton of this wavelength?

(1642–1727). While a college student, Newton became interested
in grinding lenses, light, and color. At the age of 23, Newton visited
SOLUTION
The relationship between the wavelength (λ), frequency (f ), and speed

TABLE 7.2 of light in a vacuum (c) is found in equation 7.3, c = λf.
Range of wavelengths and frequencies of the colors 8 c _

of visible light c = 3.00 × 10 m/s c = λf ∴ f =
λ
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λ = 5.60 × 10 m
Color Wavelength (in Meters) Frequency (in Hertz) 8 m _

3.00 × 10
f = ? __
s
f =
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14
Red 7.9 × 10 to 6.2 × 10 –7 3.8 × 10 to 4.8 × 10 14 5.60 × 10 m
14
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8
Orange 6.2 × 10 to 6.0 × 10 –7 4.8 × 10 to 5.0 × 10 14 _ 1 _
3.00 × 10 m _

= ×

m
14
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Yellow 6.0 × 10 to 5.8 × 10 –7 5.0 × 10 to 5.2 × 10 14 5.60 × 10 –7 s
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14
Green 5.8 × 10 to 4.9 × 10 –7 5.2 × 10 to 6.1 × 10 14 14 1 _

= 5.40 × 10
14
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Blue 4.9 × 10 to 4.6 × 10 –7 6.1 × 10 to 6.6 × 10 14 s
14
14
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Violet 4.6 × 10 to 3.9 × 10 –7 6.6 × 10 to 7.7 × 10 14 = 5.40 × 10 Hz
188 CHAPTER 7 Light 7-12