physics

Maxwell coil

Maxwell coil is a physics 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 Maxwell coil rather than just read about it. In short: A Maxwell coil is a device for producing a large volume of almost constant (or constant-gradient) magnetic field. It is named in honour of the Scottish physicist James Clerk Maxwell.

Key takeaways

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

Reference excerpt

A Maxwell coil is a device for producing a large volume of almost constant (or constant-gradient) magnetic field. It is named in honour of the Scottish physicist James Clerk Maxwell. A Maxwell coil is an improvement of a Helmholtz coil: in operation it provides an even more uniform magnetic field (than a Helmholtz coil), but at the expense of more material and complexity.

Description

A constant-field Maxwell coil set consists of three coils oriented on the surface of a virtual sphere. According to Maxwell's original 1873 design: each of the outer coils should be of radius 4 7 R {\displaystyle \textstyle {\sqrt {\frac {4}{7}}}R} , and distance 3 7 R {\displaystyle \textstyle {\sqrt {\frac {3}{7}}}R} from the plane of the central coil of radius R {\displaystyle R} . Maxwell specified the number of windings as 64 for the central coil and 49 for the outer coils. Though Maxwell did not specifically state that current for the coils came from the same source, his work was specifically describing the construction of a sensitive galvanometer designed to detect a single current source. It follows that the ampere-turns for each of the smaller coils must be exactly 49 64 {\displaystyle {\frac {49}{64}}} of the turns of the larger.

Gradient-field Maxwell coil A gradient-field Maxwell coil has essentially the same geometry of the 3-coil configuration above, but the central coil is removed to leave only the smaller two coils, and the current in one of these is reversed. This produces a uniform-gradient magnetic field near the centre of the two coils. Maxwell describes the use of the 2-coil configuration for the generation of a uniform force on a small test coil. A Maxwell coil of this type is similar to a Helmholtz coil with the coil distance increased from coil radius R {\displaystyle R} to 3 R {\displaystyle {\sqrt {3}}\,R} and the coils fed with opposite currents.

Illustrations

Worked examples

Example 1 — a first encounter with Maxwell coil

Start with the simplest possible case. Write down what Maxwell coil claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 Maxwell coil 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 Maxwell coil 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 Maxwell coil

In research: Maxwell coil appears in physics 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 Maxwell coil 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: Maxwell coil is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electromagnetic coils, Magnetic devices, so understanding it makes those chapters shorter.
In everyday life: Look for Maxwell coil 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 Maxwell coil in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Maxwell coil 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 Maxwell coil out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Maxwell coil in simple terms?

A Maxwell coil is a device for producing a large volume of almost constant (or constant-gradient) magnetic field. It is named in honour of the Scottish physicist James Clerk Maxwell.

Why does Maxwell coil matter?

Because it connects several physics 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 Maxwell coil?

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 Maxwell coil.