science

Statcoulomb

Statcoulomb 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 Statcoulomb rather than just read about it. In short: The statcoulomb (statC), franklin (Fr), or electrostatic unit of charge (esu) is the unit of measurement for electrical charge used in the centimetre–gram–second electrostatic units variant (CGS-ESU) and Gaussian systems of units. In terms of the Gaussian base units, it is That is, it is defined so that the proportionality constant in Coulomb's law using CGS-ESU quantities is a dimensionless quantity equal to 1.

Key takeaways

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

Reference excerpt

The statcoulomb (statC), franklin (Fr), or electrostatic unit of charge (esu) is the unit of measurement for electrical charge used in the centimetre–gram–second electrostatic units variant (CGS-ESU) and Gaussian systems of units. In terms of the Gaussian base units, it is

That is, it is defined so that the proportionality constant in Coulomb's law using CGS-ESU quantities is a dimensionless quantity equal to 1.

Definition and relation to CGS base units Coulomb's law in the CGS-Gaussian system takes the form

F = q 1 G q 2 G r 2 , {\displaystyle F={\frac {q_{1}^{_{\text{G}}}q_{2}^{_{\text{G}}}}{r^{2}}},}

where F is the force, qG1 and qG2 are the two electric charges, and r is the distance between the charges. This serves to define charge as a quantity in the Gaussian system. The statcoulomb is defined such that if two electric charges of 1 statC each and have a separation of 1 cm, the force of mutual electrical repulsion is 1 dyne. Substituting F = 1 dyn, qG1 = qG2 = 1 statC, and r = 1 cm, we get:

From this it is also evident that the quantity dimension of electric charge as defined in the CGS-ESU and Gaussian systems is M1/2L3/2T−1.

Conversion between systems Conversion of a quantity to the corresponding quantity of the International System of Quantities (ISQ) that underlies the International System of Units (SI) by using the defining equations of each system. The SI uses the coulomb (C) as its unit of electric charge. The conversion factor between corresponding quantities with the units coulomb and statcoulomb depends on which quantity is to be converted. The most common cases are:

For electric charge: For electric flux (ΦD): For electric flux density (D): The symbol "≘" ('corresponds to') is used instead of "=" because the two sides cannot be equated.

References

Worked examples

Example 1 — a first encounter with Statcoulomb

Start with the simplest possible case. Write down what Statcoulomb 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 Statcoulomb 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 Statcoulomb 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 Statcoulomb

In research: Statcoulomb 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 Statcoulomb 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: Statcoulomb is common in secondary-school and first-year university syllabi. It links to neighbouring topics Centimetre–gram–second system of units, Units of electrical charge, so understanding it makes those chapters shorter.
In everyday life: Look for Statcoulomb 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 Statcoulomb in 20 minutes

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

Frequently asked questions

What is Statcoulomb in simple terms?

Why does Statcoulomb 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 Statcoulomb?

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 Statcoulomb.