Study Guides/Maths/Self Inductance Formula
Study Guide · Maths

Self Inductance Formula – Definition and Derivation

Self-inductance is the property of a coil (inductor) by which it opposes any change in the electric current flowing through it, by generating an opposing EMF (electromotive force) in itself.

The fundamental formula defining self-inductance is: L = NΦ / I

Question (Click to Flip)

What is the formula for self inductance?

Answer

The self inductance L of a coil is given by L = NΦ/I (from definition), or for a solenoid, L = μ₀n²V.

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Key Facts

Definition: L = NΦ/I (Henry per turn).

SI Unit: Henry (H).

Induced EMF: ε = -L(dI/dt).

Solenoid Formula: L = μ₀n²V.

A coil with L = 1 Henry produces 1 volt when current changes at 1 A/s.

The Key Formulas

  1. Definition Formula: L = NΦ / I Where: N = number of turns, Φ = magnetic flux per turn, I = current.

  2. Induced EMF Formula: ε = -L (dI/dt) The self-induced EMF is proportional to the rate of change of current.

  3. Self Inductance of a Solenoid: L = μ₀ × n² × V Where: μ₀ = permeability of free space (4π×10⁻⁷ H/m), n = number of turns per unit length, V = volume of the solenoid (= A×l).

Factors Affecting Self-Inductance

Self-inductance L increases when:

  • The number of turns (N) is more.
  • The cross-sectional area (A) is larger.
  • The length is shorter (more tightly wound coil).
  • The core is filled with a magnetic material like iron (increases μ).

Questions and Answers

What is the formula for self inductance?+

The self inductance L of a coil is given by L = NΦ/I (from definition), or for a solenoid, L = μ₀n²V.

What is the SI unit of self inductance?+

The SI unit of self-inductance is the Henry (H).

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