EM Spectrum

The electromagnetic spectrum spans many decades of frequency (≈ 10³ to 10²² Hz) — all the same kind of wave, only λ and source differ.

Radio waves (≥ 10⁻¹ m): generated by oscillating LC circuits; used in AM/FM, TV, mobile, radar.

Microwaves (1 mm – 30 cm): produced by klystrons / magnetrons; used in radar, satellite communication, microwave ovens (resonate water at 2.45 GHz).

Infrared (700 nm – 1 mm): from hot bodies / molecular vibrations; used in thermal imaging, IR remote controls, night vision.

Visible light (400–700 nm): the narrow band the human eye detects; produced by electron transitions in atoms.

Ultraviolet (10–400 nm): from very hot sources / electron transitions; causes sunburn, fluorescence, sterilisation. Mostly absorbed by the ozone layer.

X-rays (0.01–10 nm): from sudden deceleration of high-energy electrons (bremsstrahlung) or inner-shell transitions; used in medical imaging and crystallography.

γ-rays (< 0.01 nm): from nuclear transitions and cosmic events — highest frequency, shortest λ, most penetrating, most ionising.

All EM waves travel at c in vacuum. They differ in λ and frequency — and therefore in HOW they interact with matter.