Physics · Electromagnetic Induction · NEET
No. Self-inductance is one coil reacting to its OWN changing current (flux it makes through itself). Mutual inductance is about TWO coils: a changing current in coil 1 induces an emf in a separate coil 2. Self = talking to yourself, mutual = talking to a neighbour. Both are measured in henry and both depend only on geometry, not on the current.
In M₂₁ the first number (2) is the coil where flux/emf appears, and the second number (1) is the coil carrying the current. So N₂Φ₂ = M₂₁ I₁ means: current I₁ in coil 1 produces flux linkage N₂Φ₂ in coil 2. A useful NEET fact is M₁₂ = M₂₁, so the order does not change the value.
Flux is proportional to current (Φ ∝ I), so when you divide flux linkage by current, the current cancels out. What is left, M, depends only on the shape, size, number of turns, spacing of the coils, and the material between them. Change the current and both flux and emf change, but M stays fixed — just like resistance stays fixed when you change voltage.
The henry (H). From ε = M (dI/dt), one henry means an emf of 1 volt is induced in coil 2 when the current in coil 1 changes at 1 ampere per second. So 1 H = 1 V·s/A = 1 Wb/A. This is the same unit as self-inductance.
Yes. Mutual inductance is defined between a pair of circuits — a source coil and a linked coil. If there is only one coil reacting to itself, that is self-inductance, not mutual. In NEET numericals, look for two solenoids, two loops, or a primary and secondary — that is your signal to use M.
Two conducting circular loops of radii R₁ and R₂ are placed in the same plane with their centres coinciding. If R₁ ≫ R₂, the mutual inductance M between them will be directly proportional to:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
N₂Φ₂ = M I₁, which rearranges to M = N₂Φ₂ / I₁. In words, mutual inductance equals the total flux linkage in the second coil divided by the current in the first coil. The induced emf form is ε₂ = −M (dI₁/dt).
The henry (H), where 1 H = 1 Wb/A = 1 V·s/A. It is the same unit used for self-inductance.
Number of turns of both coils, their cross-sectional area, the distance and orientation between them, and the relative permeability μᵣ of the material between them. It does NOT depend on the current.
Yes. For any pair of coils, M₁₂ = M₂₁ = M. This reciprocity is a standard NEET result, so you can compute M whichever way is easier.
It is the working principle of transformers and is a repeat topic in the Electromagnetic Induction chapter. Questions test the formula M = NΦ/I, the henry unit, and the fact that M depends only on geometry — exactly the traps NTA likes to set.
