Electromagnetic induction is the link between electricity and magnetism: a changing magnetic flux produces an e.m.f. in a coil. The induced current flows so that its own field opposes the change (Lenz law). Coils store energy in their magnetic field as $\tfrac{1}{2}LI^2$, exactly like a spring stores $\tfrac{1}{2}kx^2$.
Subpages
- Faraday laws and Lenz → — state both Faraday laws (×2), write integral and differential forms (2018), explain Lenz by energy, non-inductive coil (×2: 2018, 2023), self-induction / electric inertia (2019), $L$ and $M$ definitions (2022).
- Inductance numerics and proofs → — 800→500-turn coil (2022 → ≈156 mH), 1 m solenoid (2019 → ≈0.247 H, ≈0.49 J), 40 cm solenoid (2023 → ≈0.63 mH), parallel-coils proof (2022), 50+100→75 mH numeric (2023 → $M = 37.5$ mH), $U = \tfrac{1}{2}LI^2$ proof (×2).
Most-repeated questions
- Faraday laws statement / explanation — 2019, 2022 (×2).
- Non-inductive coil — 2018, 2023 (×2).
- Magnetic energy $U = \tfrac{1}{2}Li^2$ — 2018, 2023 (×2).
How to use
Read the Faraday page first. It gives you the laws, Lenz, and the definitions of $L$ and $M$. Then do the inductance page — every numeric on it uses $L = \mu_0 N^2 A/l$ and the scaling $L \propto N^2$ for similar coils. Master constant: $\mu_0 = 4\pi\times 10^{-7}$ H/m.
Note. The 7 questions on the borderline page appeared in old GE-2 papers but are NOT verbatim in the PHYS7021 text. Confirm with your lecturer before revising them.
Reference. Brij Lal & Subrahmanyam Ch-10; H.C. Verma Vol-1 Ch-38; S.L. Arora Vol-1 Ch-6.