radio

Radio: 

Radio

Question:: 

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: 

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

Electromagnets and Energy: 

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

Inductors: 

Inductors Inductors are electromagnets Inductors store magnetic energy Inductors oppose changes in current

Tank Circuit: 

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

Tank Circuit Oscillation: 

Tank Circuit Oscillation

Tank Circuits in Radio: 

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

Emitting Radio Waves 1: 

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

Emitting Radio Waves 2: 

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

Structure of a Radio Wave: 

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

AM Modulation: 

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

FM Modulation: 

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

Question:: 

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