area perpendicular to the line of solar flux at the top of the atmosphere receives energy at a rate of 1, 340 watts, sufficient, for example, to power an electric iron This is called the solar flux(see Chapter 9, Figure 9.3) Light and electromagnetic Radiation lectromagnetic radiation, particularly light, is of utmost importance in considering energy in environmental systems. Therefore, the following important points related to electromagnetic radiation should be noted Energy can be carried through space at the speed of light(c), 3.00 x 108 meters per second(m/s)in a vacuum, by electromagnetic radiation which includes visible light, ultraviolet radiation, infrared radiation, icrowaves, radio waves, gamma rays, and X-rays Electromagnetic radiation has a wave character. The waves move at the speed of light, c, and have characteristics of wavelength(2), amplitude, and frequency(v, Greek nu")as illustrated below AAAA-wfAA The wavelength is the distance required for one complete cycle, and the frequency is the number of cycles per unit time. They are related by the where v is in units of cycles per second(s", a unit called the hertz, Hz) andλ Is In meters(m) In addition to behaving as a wave, electromagnetic radiation has char acteristics of particle The dual wave/particle nature of electromagnetic radiation is the basis of the quantum theory of electromagnetic radiation, which states that radiant energy may be absorbed or emitted only in discrete packets called quanta or photons. The energy, E, of each photon is given by where h is Plancks constant, 6.63 x 10-34 J-s joule x second) From the preceding, it is seen that the energy of a photon is higher when the frequency of the associated wave is higher(and the wavelength shorter) C 2000 CRC Press llcarea perpendicular to the line of solar flux at the top of the atmosphere receives energy at a rate of 1,340 watts, sufficient, for example, to power an electric iron. This is called the solar flux (see Chapter 9, Figure 9.3). Light and Electromagnetic Radiation Electromagnetic radiation, particularly light, is of utmost importance in considering energy in environmental systems. Therefore, the following important points related to electromagnetic radiation should be noted: • Energy can be carried through space at the speed of light (c), 3.00 x 108 meters per second (m/s) in a vacuum, by electromagnetic radiation, which includes visible light, ultraviolet radiation, infrared radiation, microwaves, radio waves, gamma rays, and X-rays. • Electromagnetic radiation has a wave character. The waves move at the speed of light, c, and have characteristics of wavelength (l), amplitude, and frequency (n, Greek “nu”) as illustrated below: Amplitude Wavelength Shorter wavelength. higher frequency • The wavelength is the distance required for one complete cycle, and the frequency is the number of cycles per unit time. They are related by the following equation: nl = c where n is in units of cycles per second (s-1, a unit called the hertz, Hz) and l is in meters (m). • In addition to behaving as a wave, electromagnetic radiation has char￾acteristics of particles. • The dual wave/particle nature of electromagnetic radiation is the basis of the quantum theory of electromagnetic radiation, which states that radiant energy may be absorbed or emitted only in discrete packets called quanta or photons. The energy, E, of each photon is given by E = h n where h is Planck’s constant, 6.63 ´ 10-34 J-s (joule ´ second). • From the preceding, it is seen that the energy of a photon is higher when the frequency of the associated wave is higher (and the wavelength shorter). © 2000 CRC Press LLC