Electromagnetic Waves

About this unit

This short unit completes the story of electricity and magnetism. Faraday showed that a changing magnetic field produces an electric field; Maxwell added the idea that a changing electric field produces a magnetic field, through what he called displacement current. Together these two effects allow electric and magnetic fields to sustain each other and travel through empty space as electromagnetic waves, at the speed of light. The unit first explains displacement current and the properties of electromagnetic waves, and then surveys the electromagnetic spectrum from radio waves to gamma rays, with the sources and uses of each band.

How to prepare

Learn the expression for displacement current and why it was needed for a charging capacitor. Memorise c = 1/√(μ₀ε₀), E₀/B₀ = c and the directions of E, B and propagation. Learn the spectrum in order of wavelength with one source and two uses for each band. Practise c = fλ conversions and quick numericals on capacitor displacement current.