ELECTROMAGNETIC WAVES – COMPLETE EXAM
NOTES (NCERT Class XII)
1. Nature of Electromagnetic Waves
• Transverse waves consisting of oscillating electric (E) and magnetic (B) fields.
• Do not require material medium; propagate in vacuum.
• Produced by accelerated or oscillating charges.
2. Displacement Current and Ampere–Maxwell Law
• Maxwell introduced displacement current to ensure current continuity in a charging capacitor.
Displacement current: Id = ε■ dΦE / dt
Ampere–Maxwell Law: ■ B · dl = µ■ ( I + Id )
• During charging of capacitor: I = Id
• Fully charged capacitor (DC): I = 0 and Id = 0
3. Speed and Field Relations
Speed in vacuum: c = 1 / √( µ■ ε■ ) = 3 × 10■ m s■¹
Speed in medium: v = 1 / √( µ ε )
Relation between field amplitudes: E■ = c B■
• Frequency of an EM wave remains unchanged when it enters a medium.
4. Diagram: Plane EM Wave Propagating Along X-axis
