Electromagnetic Waves — Part 2: The electromagnetic spectrum: visual lesson, CBSE Class 12 Physics

Lesson

The electromagnetic spectrum

Part 2 — one family of waves, from kilometre-long radio waves to gamma rays smaller than an atomic nucleus.

In this lesson you will

Arrange the bands of the electromagnetic spectrum in order of wavelength and frequency
State how each band is produced and give its uses
Use c = fλ to place a wave in the spectrum

Band edges are approximate; the bands overlap slightly in practice.

Diagram

The spectrum at a glance

Band edges are approximate; the bands overlap slightly in practice.

All bands travel at $c$ in vacuum and obey $c = f\lambda$ : shorter wavelength means higher frequency (and higher photon energy, Chapter 11). The bands have no sharp edges; neighbouring bands overlap.

Concept

Bands, sources and uses

Each band is produced and detected in a characteristic way:

Table of the seven bands of the electromagnetic spectrum with approximate wavelength ranges, how each is produced and typical uses
Band	Wavelength (approx.)	Produced by	Typical uses
Radio	0.1 m	Accelerated charges in aerials	Radio, TV, mobile phones
Microwave	0.1 m to 1 mm	Magnetron and klystron valves	Radar, ovens, satellite links
Infrared	1 mm to 700 nm	Hot bodies, molecular vibrations	Remote controls, night vision, physiotherapy
Visible	700 nm to 400 nm	Electron transitions in atoms	Vision, photography
Ultraviolet	400 nm to 1 nm	The Sun, arc lamps	Sterilisation, LASIK surgery
X-rays	1 nm to 1 pm	Fast electrons hitting metal targets	Medical imaging, crystal studies
Gamma rays	< 1 pm (roughly)	Nuclear reactions and decay	Cancer therapy, sterilising equipment

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