Displacement current Id = ε_{0}(dΦ_E/dt): not real charge flow; introduced by Maxwell to fix Ampere's law for capacitors; equals conduction current in wire; produces magnetic field.

EM wave properties: transverse; E ⊥ B ⊥ propagation; E and B IN phase; $E_{0}$/$B_{0}$ = c; ALL waves travel at c = $3 \times 10^{8}$ m/s in vacuum regardless of frequency.

Spectrum order (increasing frequency): Radio → Microwave → IR → Visible → UV → X-ray → Gamma. Mnemonic: "Rich Men In Visible Uniforms eXude Glamour."

X-ray vs Gamma: overlapping frequency ranges; distinguished by source only (electron deceleration vs nuclear decay).

Key applications: Microwave = RADAR/ovens; UV = sterilisation/LASIK; IR = night vision; X-ray = bone imaging; Gamma = cancer treatment.