Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

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Revised Pages

19.2 Electromagnetic Radiation • 761

108

Energy (eV) Wavelength (m)

1 angstrom (Å)

Violet

Blue

Green

Yellow

Orange

Red

0.7 m

0.6 m

0.5 m

0.4 m

Visible spectrum

wavelength

1 nanometer (nm)

1 micrometer (m)

1 millimeter (mm)

1 meter (m)

1 kilometer (km)

Frequency (Hz)

106

104

102

100

10 –2

10 –4

10 –6

10 –8

10 –10

1022

1020

1018

1016

1014

1012

1010

108

106

104

10 –14

10 –12

10 –10

10 –8

10 –6

10 –4

10 –2

100

102

104

-Rays

X-Rays

Ultraviolet

Infrared

Microwave

Radio, TV

–Visible

Figure 19.2 The

spectrum of

electromagnetic

radiation, including

wavelength ranges

for the various colors

in the visible

spectrum.

Visible light lies within a very narrow region of the spectrum, with wavelengths

ranging between about 0.4μm(4× 10 −^7 m) and 0.7μm. The perceived color

is determined by wavelength; for example, radiation having a wavelength of ap-

proximately 0.4μm appears violet, whereas green and red occur at about 0.5 and

0.65μm, respectively. The spectral ranges for the several colors are included in Figure

19.2. White light is simply a mixture of all colors. The ensuing discussion is concerned

primarily with this visible radiation, by definition the only radiation to which the eye

is sensitive.

All electromagnetic radiation traverses a vacuum at the same velocity, that of

light—namely, 3× 108 m/s (186,000 miles/s). This velocity,c, is related to the electric

For a vacuum, permittivity of a vacuum 0 and the magnetic permeability of a vacuumμ 0 through

dependence of the

velocity of light on

electric permittivity

and magnetic

permeability

c=

1

√

 0 μ 0

(19.1)

Thus, there is an association between the electromagnetic constantcand these elec-

trical and magnetic constants.

Furthermore, the frequencyνand the wavelengthλof the electromagnetic ra-

For electromagnetic diation are a function of velocity according to

radiation,

relationship among

velocity, wavelength,

and frequency

c=λν (19.2)

Frequency is expressed in terms of hertz (Hz), and 1 Hz=1 cycle per second. Ranges

of frequency for the various forms of electromagnetic radiation are also included in

the spectrum (Figure 19.2).