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Unformatted text preview: Maxwell's equations) at speed c . Therefore, the power incident on an area perpendicular to the direction of travel will have an amount of energy flow through it every second of uc . This can be seen from the dimensions of energy/volume distance/second = energy per area per second. This is the incident power, S . Thus, S = uc = = c 2 EB . We can express this more usefully as a vector , perpendicular to and and normal to the surface across which the power per unit area is being calculated. This gives: This is called the Poynting vector. Figure %: Direction of propagation of an electromagnetic wave. Thus light is a form of electromagnetic radiation, just like radiowaves, microwaves, infrared rays, X-rays, gamma rays and cosmic rays. It has frequencies in the range 3.8410 14 Hz to 7.6910 14 Hz, which corresponds to wavelengths of 780 to 390 nanometers....
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