Permeance

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Permeance is a measure of how easily something passes through a material. It’s usually represented by the letter P.

In electromagnetism, permeance is the inverse of reluctance. In a magnetic circuit, it tells you how much magnetic flux you get for a given magnetomotive force. The idea is similar to electrical conductance: a larger cross‑section or a shorter path increases permeance.

Key relationships:
- P = 1 / R, where R is reluctance.
- P = Φ / F, where Φ is magnetic flux and F is magnetomotive force. Since F = N I (N turns, I current), P = Φ / (N I).

In terms of material properties, permeance can also be written as P = μ A / ℓ, where μ is permeability, A is cross‑sectional area, and ℓ is the path length.

Unit: henry (H), equivalently webers per ampere.

In materials science, permeance can also mean how readily a material transmits another substance.