6.2.7Waves
Radio Waves — AQA GCSE Combined Science Trilogy 8464 - Physics Revision Notes & Topical Questions
5 min read 6 parts Lesson 13 of 15
Part 1 of 4Producing and detecting radio waves
1
An alternating current in a transmitter circuit makes electrons in the aerial oscillate. Each oscillation produces a radio wave of the same frequency.
2
The wave carries a signal, encoded by varying either its amplitude or its frequency.
3
The wave spreads out and travels at the speed of light, 3 × 108 m/s in air.
4
When the wave reaches a receiving aerial, it is absorbed and makes electrons oscillate, producing an alternating current with the same frequency as the wave (HT only).
5
The receiver processes this current to recover the sound, picture or data.
Part 2 of 4Uses of radio waves
| Use | Why radio waves suit it |
|---|---|
| Radio and television broadcasting | Long wavelengths diffract around hills and obstacles; the waves travel long distances |
| Bluetooth and Wi-Fi | Short-range signals carry data between devices without wires |
| Mobile phones | High-frequency waves carry lots of data to nearby masts |
| Satellite communication | Signals can pass through the atmosphere to satellites |
| RFID tags | A reader activates a small tag without direct contact |
Part 3 of 4Transmission routes
How signals reach the receiver
Ground waves
- Ground waves Low-frequency waves follow the curve of the Earth and reach beyond the horizon.
Sky waves
- Sky waves Some radio waves are reflected by the ionosphere, so signals can travel around the world.
Line of sight
- Line of sight Short wavelengths such as those for TV and phones travel in straight lines, so aerials must see each other.
Satellite
- Satellite Microwaves pass through the atmosphere and are relayed by satellites in orbit.
Part 4 of 4Safety and properties
Lowest frequency
- Lowest frequency Radio waves have the longest wavelengths in the EM spectrum, from about 1 m to over 10 km, and the lowest frequencies and energy.
Little absorption
- Little absorption They are not strongly absorbed by the body, so exposure at normal levels is considered low risk.
Interference
- Interference Two stations on similar frequencies can interfere, so each station is given its own frequency.
Key terms
| Term | Meaning |
|---|---|
| Radio wave | An EM wave with the longest wavelength and lowest frequency. |
| Transmitter | A device that generates and sends out radio waves. |
| Receiver | A device that detects radio waves and converts them to a signal. |
| Aerial | A conductor in which oscillating charges send or receive radio waves. |
| Ionosphere | A layer of the upper atmosphere that reflects some radio waves. |
Avoid these mistakes
1
Saying that radio waves are sound waves. They are electromagnetic and need no medium.
2
Stating that the receiving aerial makes the wave. It absorbs the wave and a current is induced.
3
Mixing up amplitude and frequency modulation.
4
Forgetting that the frequency of the induced current equals the frequency of the incoming wave.
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