science

Permeance

Permeance is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Permeance rather than just read about it. In short: Permeance, in general, is the degree to which a material admits a flow of matter or energy. Permeance is usually represented by a curly capital P: P.

Key takeaways

Permeance belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Permeance to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Permeance from memory before moving on to harder problems.

Reference excerpt

Permeance, in general, is the degree to which a material admits a flow of matter or energy. Permeance is usually represented by a curly capital P: P.

Electromagnetism In electromagnetism, permeance is the inverse of reluctance. In a magnetic circuit, permeance is a measure of the quantity of magnetic flux for a number of current-turns. A magnetic circuit almost acts as though the flux is conducted, therefore permeance is larger for large cross-sections of a material and smaller for smaller cross section lengths. This concept is analogous to electrical conductance in the electric circuit. Magnetic permeance P is defined as the reciprocal of magnetic reluctance R (in analogy with the reciprocity between electric conductance and resistance):

P = 1 R {\displaystyle {\mathcal {P}}={\frac {1}{\mathcal {R}}}}

which can also be re-written:

P = Φ B N I {\displaystyle {\mathcal {P}}={\frac {\Phi _{\mathrm {B} }}{NI}}}

using Hopkinson's law (magnetic circuit analogue of Ohm's law for electric circuits) and the definition of magnetomotive force (magnetic analogue of electromotive force):

F = Φ B R = N I {\displaystyle {\mathcal {F}}=\Phi _{\mathrm {B} }{\mathcal {R}}=NI}

where:

ΦB, magnetic flux, I, current, in amperes, N, winding number of, or count of turns in the electric coil. Alternatively in terms of magnetic permeability (analogous to electric conductivity):

P = μ A ℓ {\displaystyle {\mathcal {P}}={\frac {\mu A}{\ell }}}

where:

μ, permeability of material, A, cross-sectional area, ℓ, magnetic path length. The SI unit of magnetic permeance is the henry (H), equivalently, webers per ampere.

Materials science In materials science, permeance is the degree to which a material transmits another substance.

See also Dielectric complex reluctance Reluctance

Notes

References

Electromagnetism Properties of Magnetic Materials Archived 2006-10-02 at the Wayback Machine (units of magnetic permeance)

Material science Bombaru, D., Jutras, R., and Patenaude, A., "Air Permeance of Building Materials". Summary report prepared by, AIR-INS Inc. for Canada Mortgage and Housing Corporation, Ottawa, 1988.

Illustrations

Worked examples

Example 1 — a first encounter with Permeance

Start with the simplest possible case. Write down what Permeance claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Permeance before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Permeance ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Permeance

In research: Permeance appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Permeance in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Permeance is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electric and magnetic fields in matter, so understanding it makes those chapters shorter.
In everyday life: Look for Permeance outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Permeance in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Permeance means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Permeance out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Permeance in simple terms?

Permeance, in general, is the degree to which a material admits a flow of matter or energy. Permeance is usually represented by a curly capital P: P.

Why does Permeance matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Permeance?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Permeance.