Electromagnetic Waves

Maxwell’s fix to Ampère’s law: a changing E field acts like a current, even where no charge actually crosses (e.g. between capacitor plates).

1. Gauss’s law (E): field lines start/end on charge.
2. Gauss’s law (B): no magnetic monopoles — net flux always zero.
3. Faraday’s law: changing B induces a circulating E.
4. Ampère–Maxwell law: current or changing E induces a circulating B.

1. Transverse: E, B, and direction of propagation are mutually perpendicular.
2. E and B oscillate in phase; amplitude ratio $E_0/B_0 = c$.
3. Need no medium; travel through vacuum at $c \approx 3\times10^8$ m/s.
4. Carry both energy and momentum (radiation pressure).

Given either f or λ, the other is fixed. Don’t memorise band wavelengths, compute them.

1. Radio (f < 3×10⁹ Hz, λ > 10 cm): broadcasting, communication.
2. Microwave (3×10⁹–3×10¹¹ Hz): radar, microwave ovens.
3. Infrared (3×10¹¹–4×10¹⁴ Hz): thermal imaging, remote controls.
4. Visible (4×10¹⁴–7.5×10¹⁴ Hz): human sight — a razor-thin sliver of the full spectrum.
5. Ultraviolet (7.5×10¹⁴–3×10¹⁶ Hz): sterilisation; causes tanning/skin damage.
6. X-ray (3×10¹⁶–3×10¹⁹ Hz): medical & structural imaging.
7. Gamma (f > 3×10¹⁹ Hz): nuclear processes, cancer treatment, ionising/hazardous.

See it live: interactive spectrum simulation →