Physics · Electromagnetic Induction · NEET
No. This is the most common confusion. From L = NΦ/I it looks like L depends on I, but flux linkage NΦ itself is proportional to I (NΦ ∝ I). So when I doubles, NΦ also doubles and the ratio L stays exactly the same. L is a constant fixed by the coil's geometry (number of turns, area, length) and the core material's permeability. Current is not a factor at all.
Φ is the magnetic flux through ONE single turn of the coil. Flux linkage is NΦ, the total flux summed over all N turns. Self-inductance uses the total flux linkage: NΦ = LI. So if a PYQ gives you 'flux linked with each turn', you must multiply by N before dividing by I. Missing this multiplication is a classic mistake.
NCERT says self-inductance 'plays the role of inertia'. In mechanics, mass resists a change in velocity. In a coil, self-inductance resists a change in current: the moment current tries to change, L produces a back emf ε = -L dI/dt that opposes that change. A large L means the current is hard to switch on or off quickly, just like a heavy mass is hard to speed up or stop.
When people say just 'inductance' for a single coil, they usually mean self-inductance. The word inductance is the broader idea; it splits into self-inductance (a coil affecting itself) and mutual inductance (one coil affecting a nearby coil). Both are measured in the same unit, the henry (H).
The SI unit is the henry (H). From ε = -L dI/dt, 1 henry = 1 volt-second per ampere (V·s/A). A coil has L = 1 H if a current changing at 1 A/s induces a back emf of 1 V in it. From L = NΦ/I, it also equals 1 weber per ampere (Wb/A).
A long solenoid has 1000 turns. When a current of 4 A flows through it, the magnetic flux linked with each turn of the solenoid is 4 × 10⁻³ Wb. The self-inductance of the solenoid is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the property of a coil to oppose any change in the current passing through itself. When current changes, the coil sets up its own back emf to slow that change. The measure of this opposition is L, in henry.
Two forms are used in NEET. From flux: L = NΦ/I (total flux linkage per unit current). From back emf: ε = -L dI/dt, so L = -ε/(dI/dt). For a long solenoid, L = μ₀ n² A l.
Only three things: the geometry of the coil (number of turns, cross-sectional area, length), and the permeability of the core material (μ₀ for air, μ = μ_r μ₀ for iron). It does NOT depend on the current or the applied voltage.
The henry (H). 1 H = 1 V·s/A = 1 Wb/A. A coil is 1 henry if a current changing at 1 A/s gives a 1 V back emf.
When current in the coil changes, its own magnetic flux changes. By Faraday's law an emf is induced, and by Lenz's law it opposes the change. This self-induced emf ε = -L dI/dt is called back emf because it works against the source.
