This chapter joins electricity and magnetism into one theory. A changing electric field makes a magnetic field. A changing magnetic field makes an electric field. Together they travel as a wave — light.
This chapter has two detailed pages. Read them in order.
- 4A · Maxwell Equations + Wave Equation — conduction vs displacement current, Ampere law for non-steady currents, all four Maxwell equations, wave equation with $c = 1/\sqrt{\varepsilon_0\mu_0}$.
- 4B · EM Waves: Energy, Numerics, Verification — Poynting vector, refractive-index numerics with full division work, EM wave properties, checking a given $\vec{E}$, $\vec{B}$ pair.
How to study this chapter
First learn the four Maxwell equations by name: Gauss-E, Gauss-B, Faraday, Ampere–Maxwell. Then learn how two curl equations combine to give a wave. Then do the numerics on speed, wavelength and the Poynting vector.
Most-repeated questions (both pages)
- Write down Maxwell equations — ×5 across 2018, 2019, 2020, 2022, 2023.
- Refractive-index and velocity/wavelength numerics (water $n = 1.33$, glass $n = 1.658$, $\lambda_0 = 5893$ Å) — ×3 in 2022, 2023, 2024.
- Define Poynting vector (with unit) — ×3 in 2018, 2019, 2022.
- Derive the EM wave equation in free space — ×2 in 2018, 2022.
Every exam asks at least one question from this chapter.
Reference. Brij Lal & Subrahmanyam Ch-11; Ajoy Ghatak Ch-7.