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Radio

Explore the fascinating world of radio waves, where electrically charged objects create electromagnetic fields that can transmit sound over vast distances without wires. Discover how antennas play a crucial role in both transmitting and receiving signals, the significance of frequency modulation (FM) and amplitude modulation (AM) in encoding information, and how tank circuits facilitate the emission and detection of radio waves. Learn about the interactions between electric and magnetic fields and the principles of inductors and electromagnets that power our communications.

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Radio

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Presentation Transcript

  1. Radio

  2. Introductory 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 backand forth throughinductor • Energy shifts backand 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 (Part 1) • A transmitter uses a tank circuit to “slosh” charge up and down its antenna • A receiver uses a tank circuit todetect charge “sloshing” on itsantenna • Transmitter antenna chargeaffects receiver antenna charge

  10. Emitting Radio Waves (Part 1) • 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 createsmagnetic field andvice versa • Electric field determinespolarization of the wave

  12. AM Modulation • Information is encoded in the fluctuating amplitude of the wave • Pressure variations causechanges in the amount ofcharge moving on theantenna

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

  14. Introductory Question (revisited) • 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

  15. Figures

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