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EM radiation

EM radiation. Electromagnetic radiation is energy that is propagated through free space or through a material medium in the form of electromagnetic waves, such as radio waves, visible light, and gamma rays. The term also refers to the emission and transmission of such radiant energy.

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EM radiation

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  1. EM radiation • Electromagnetic radiation is energy that is propagated through free space or through a material medium in the form of electromagnetic waves, such as radio waves, visible light, and gamma rays. The term also refers to the emission and transmission of such radiant energy. • James Clerk Maxwell was the first to predict the existence of electromagnetic waves. In 1864 he set forth his electromagnetic theory, proposing that light - including various other forms of radiant energy - is an electromagnetic disturbance in the form of waves. In 1887 Heinrich Hertz, a German physicist, provided experimental confirmation by producing the first man-made electromagnetic waves and investigating their properties. Subsequent studies resulted in a broader understanding of the nature and origin of radiant energy. • Hertz did not realize the practical importance of his experiments. He stated that • "It's of no use whatsoever[...] this is just an experiment that proves Maestro Maxwell was right - we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there.” • Asked about the ramifications of his discoveries, Hertz replied: • "Nothing, I guess.” • There are many sources of electromagnetic radiation, both natural and man-made. Radio waves, for example, are produced by cosmic objects such as pulsars and quasars and by electronic circuits. Sources of ultraviolet radiation include mercury vapor lamps and high-intensity lights, as well as the Sun. The latter also generates X rays, as do certain types of particle accelerators and electronic devices. Heinrich Rudolf Hertz (1857-1894)

  2. We shall assume in the following that the source is localized near the origin: The total radiated power is The area of the sphere ~r2, static electric field falls off like 1/r2 (or faster), and magnetostatic field falls off like 1/r2 (or faster). Hence, static sources do not radiate. The time-dependent EM fields are responsible for radiation! Dipole radiation

  3. Electric dipole radiation Now we assume that

  4. At large distances, i.e., for (radiation zone), the second term dominates What is the vector potential of radiating dipole?

  5. What are the fields? This is a monochromatic wave of frequency w traveling in the radial direction at the speed of light. E and B fields are in phase, mutually perpendicular, and transverse.

  6. The time-averaged intensity is … and the total power radiated is:

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