Electromagnetic Waves: Radio, Radar and Television
A changing electric field creates a magnetic field, which creates an electric field — and the pattern runs off into space at the speed of light.
Big Idea: An electromagnetic (EM) wave is a self-sustaining ripple of electric and magnetic fields that travels through empty space at c = 3 × 108 m/s. Nothing material moves along with it; only the fields oscillate. These waves carry energy and information, and by making them, guiding them and detecting them we built radio, radar, television and every mobile network on the planet.
By the end you will be able to:
- explain how an oscillating charge radiates an EM wave and why the wave is transverse,
- use c = λf to connect wavelength, frequency and speed,
- define the energy flux density (intensity) of a wave and use I = P/(4πr2),
- describe the principles of radio communication — the carrier, modulation, resonant tuning and detection,
- explain how radar measures distance with d = ct/2, and how television sends a picture.