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Radio

Radio. Question:. If you took an electrically charged ball and shook it up and down rapidly, charges in a nearby metal object would move in response. How far away could that metal object be and still respond? 1 meter 1 kilometer The other side of the universe. Observations About Radio.

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Radio

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  1. Radio

  2. Question: If you took an electrically charged ball and shook it up and down rapidly, charges in a nearby metal object would move in response. How far away could that metal object be and still respond? • 1 meter • 1 kilometer • The other side of the universe

  3. Observations About Radio • Transmit sound long distances without wires • Involve antennas • Seem to involve electricity and magnetism • Reception depends on antenna positioning • Reception weakens with distance • Two styles of radio: AM and FM

  4. Electromagnets and Energy • Electric and magnetic fields contain energy • An electromagnet stores magnetic energy • Electromagnet consumes energy as it turns on • Current temporarily experiences a voltage drop • Electromagnet releases energy as it turns off • Current temporarily experiences a voltage rise • Electromagnet opposes current charges

  5. Inductors • Inductors are electromagnets • Inductors store magnetic energy • Inductors oppose changes in current

  6. Tank Circuit • Inductor & Capacitor share energy • Charge flows back and forth through inductor • Energy shifts back and forth between the two devices

  7. Tank Circuit Oscillation

  8. Tank Circuits in Radio • Tanks are resonant devices • Tanks build up energy at a specific frequency • Tanks help radios emit radio waves • Tanks help radios detect radio waves

  9. Emitting Radio Waves 1 • A transmitter uses a tank circuit to “slosh” charge up and down its antenna • A receiver uses a tank circuit to detect charge “sloshing” on its antenna • Transmitter antenna charge affects receiver antenna charge

  10. Emitting Radio Waves 2 • Accelerating charge emits radio waves • Charge produces electric field • Current produces magnetic field • Changing current produces changing magnetic field, produces changing electric field, prod… • A radio wave consists only of an electric and magnetic field • A radio wave travels through empty space at the speed of light

  11. Structure of a Radio Wave • Electric field is perpendicular to magnetic field • Electric field creates magnetic field and vice versa • Electric field determines polarization of the wave

  12. AM Modulation • Information is encoded in the fluctuating amplitude of the wave • Pressure variations cause changes in the amount of charge moving on the antenna

  13. FM Modulation • Information is encoded in the exact frequency of the charge motion • Pressure variations cause slight shifts in the frequency of charge motion on the antenna

  14. Question: If you took an electrically charged ball and shook it up and down rapidly, charges in a nearby metal object would move in response. How far away could that metal object be and still respond? • 1 meter • 1 kilometer • The other side of the universe

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