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Electromagnetic Waves

NCERT Class 12 Physics Chapter 8

Electromagnetic Waves for Class 12 Physics, JEE and NEET: displacement current, the nature of electromagnetic waves and the electromagnetic spectrum.

3 topics Updated 8 Nov 2026

For: Class 12, JEE and NEET

In the syllabus: JEE Class 12 syllabus, NEET Class 12 syllabus

With your textbook

NCERT Physics Part I (Class 12), Chapter 8 “Electromagnetic Waves”, reprint 2026-27.

Open the official NCERT chapter (PDF, 1.4 MB, ncert.nic.in)

Checked on 19 Oct 2026.

Learn in this order

  1. Displacement current

    Derivation for a charging capacitor, id = ε dΦE/dt, vs conduction current, Ampere–Maxwell law, examples.

    NCERT Sections 8.1–8.2 13 min read 4 solved examples 7 practice questions

  2. Electromagnetic waves

    Sources, properties, transverse nature, speed c = 1/√(με), B = E/c, energy, with solved examples.

    NCERT Section 8.3 17 min read 4 solved examples 7 practice questions

  3. Electromagnetic spectrum

    Radio waves to gamma rays, NCERT Table 8.1’s wavelength ranges, sources, uses and photon energies.

    NCERT Section 8.4 16 min read 4 solved examples 7 practice questions

Key formulas in this chapter

Displacement current

  • id = ε0 dΦE/dt
  • id = C dV/dt
  • i = ic + id
  • ∮ B · dl = μ0 ic + μ0 ε0 dΦE/dt

Electromagnetic waves

  • Ex = E0 sin(kz − ωt), By = B0 sin(kz − ωt)
  • k = 2π/λ, ω = ck
  • c = 1/√(μ0 ε0)
  • c = νλ
  • B0 = E0/c
  • v = 1/√(με)
  • average energy density = ½ ε0 E0^2
  • intensity I = ½ ε0 E0^2 c (beyond NCERT)
  • momentum p = U/c (beyond NCERT Chapter 8)

Electromagnetic spectrum

  • c = νλ
  • E = hν = hc/λ
  • hc ≈ 1240 eV nm

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