 the frequency, the frequency can be defined in terms of the speed of light divided by the wavelength. This gives Just as we computed the wavelength in terms of varying frequency, we can also compute frequency in terms of varying speed of the light TABLE 2.1 Prefix Meaning Common Prefixes of the Powers of 10 1/1,000,000,000,000 trillionth 1/1,000,000,000 billionth micro 1/1,000,000 millionth milli 1/1000 thousandth thousand 1,000,000 million 1,000,000,000 billion 1,000,000,000,000 trillion 1,000,000,000,000,000 quadrillion Chapter Two constant. Thus, we can compute frequency in terms of a wavelength in meters as follows: f(Hz) = 1 (m) f(MHz) = = 1 0.3 (m) 0.0003 Although we normally want to be precise in the computations we make, in the world of communications there are several rules of thumb that can be used to expedite computations. For metric computations, you can estimate the wavelength in centimeters as follows: (cm) FIGHZ = The Frequency Spectrum Using our preceding discussion of frequency and wavelength, let's look once more at the electromagnetic radiation spectrum, which is more generally referred to as the frequency spectrum. By doing this we can bet- ter comprehend the relationship between light and other types of elec- tromagnetic waves, such as audible conversations, AM and FM (ampli- tude and frequency modulation) radio, different types of television broadcasts, and microwave and infrared communications. Figure 2.3 illustrates, among other things, the locations of popular types of communication in the known frequency spectrum. The left lerstanding Light side of Figure 2.3 indicates the frequency in powers of hertz; the right side, the wavelength in terms of fractions of a meter. If you carefully examine Figure 2.3, you will note that visible light appears in the micrometer (um) wavelength region, where red light has a wavelength of 0.68 um. In many physics books the wavelength of visible light is listed in terms of nanometers (nm), where one nanometer equals one thousand millionths, e 2.3 FREQUENCY 