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Antennas

Antennas. A free charge has a constant electric field and no magnetic field. No waves are produced. No radiation. A charge at constant velocity has both fields. Fields are constant so no wave forms. B field surrounds electric field, although there is no “current” flowing here. Free Charge.

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Antennas

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  1. Antennas

  2. A free charge has a constant electric field and no magnetic field. No waves are produced. No radiation A charge at constant velocity has both fields. Fields are constant so no wave forms. B field surrounds electric field, although there is no “current” flowing here Free Charge

  3. An AC power source creates an oscillating current. The charges in the conductor accelerate. This produces a changing electric field. Creates changing magnetic field Produces EM wave. This is an antenna. Accelerating Charge

  4. A conductor in an electric field will have a current. Charges accelerate An oscillating field generates an oscillating current. Antennas must be of a length appropiate to detect the oscillation. Receiving Waves

  5. The conductor works best when parallel with the electric field. At an angle the effective field is reduced. Angled Antenna

  6. Radio Waves • Radio waves are a type of electromagnetic wave. • Broadcast antennas put out electric and magnetic fields.

  7. A radio station broadcasts FM signals at 93.9 MHz. Find the wavelength of the electromagnetic wave. First assume that the speed is the speed in a vacuum c. The speed of a wave is related to the wavelength and frequency. v = lf Solve for the wavelength. Speed of light Frequency f = 9.39 x 107 /s l= c/f l = 3.19 m Antennas should be slightly shorter than size to work well. Wavelength next

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