Electric charge: Difference between revisions
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== Charge density == | |||
For a thin, long conductor (e.g., electric cable): | |||
$$\text{charge density } \lambda = \frac{dQ}{dL}$$ | |||
For a thin surface (e.g., aluminium foil): | |||
$$\text{charge density } \sigma = \frac{dQ}{dA}$$ | |||
Latest revision as of 06:33, 2 October 2026
Electrical charge is a fundamental property of matter.
SI Unit
The SI unit of electrical charge is Coulomb (C), named after French physicist Charles Augustine de Coulomb.[1]
Charge of subatomic particles
| Particle | Symbol | Absolute charge (Coulombs) | Relative charge (to proton) |
|---|---|---|---|
| proton | $p^+$ | $+1.602 \times 10^{-19}$ | +1 |
| neutron | $n^0$ | 0 | 0 |
| electron | $e^-$ | $-1.602 \times 10^{-19}$ | −1 |
Properties
Quantisation
Any electrical charge is a whole multiple of $e \equiv 1.602 \cdot 10^{-19} C$.[1]
i.e.,
$$ \forall Q, Q=ae, a \in Z $$
Restricted type
A charge must be either positive or negative.[1]
Positive and negative charges can cancel each out, therefore the total charge of a system is the algebraic sum of charges of all its elements.[1]
i.e., $$ Q_{system}=\sum Q_{element} $$
Warning: This does not mean the entire system can be always approximated as a point charge of $\sum Q_{elements}$, as the distribution of charges heavily influence the electrostatic behaviour of a system.
Conservation
Charge can neither be created or destroyed but only transfered. The amount of charge in any closed system is constant.[1]
i.e.,
$$\sum Q = C$$
where C is a constant for any closed system.
Electrostatic force
Any charge exert an electrostatic force on any other charge.[1]
This phenomenon is described by Coulomb's law:
$$\vec F_{e}(B \to A)=-\frac{1}{4\pi \epsilon_0}\frac{Q_AQ_B}{\left\| AB \right\|^2}\widehat{AB}$$
where $A$,$B$ are point charges
Charge density
For a thin, long conductor (e.g., electric cable):
$$\text{charge density } \lambda = \frac{dQ}{dL}$$
For a thin surface (e.g., aluminium foil):
$$\text{charge density } \sigma = \frac{dQ}{dA}$$
- ↑ ↑ ↑ ↑ ↑ ↑ OpenStax. (2025). 5.2: Electric Charge. LibreTexts. https://phys.libretexts.org/Bookshelves/University_Physics/University_Physics_(OpenStax)/University_Physics_II_-_Thermodynamics_Electricity_and_Magnetism_(OpenStax)/05%3A_Electric_Charges_and_Fields/5.02%3A_Electric_Charge
- ↑ LibreTexts. (n.d.). 1.2: Structure of the Atom. LibreTexts. Retrieved https://chem.libretexts.org/Courses/Chabot_College/Chem_12A%3A_Organic_Chemistry_Fall_2022/01%3A_Introduction_to_Organic_Chemistry-_review_of_atoms_and_molecules/1.02%3A_Structure_of_the_Atom
- ↑ LibreTexts. (n.d.). 3.5: The Atomic Nucleus. LibreTexts. Retrieved https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary)/03%3A_Atomic_Structure/3.05%3A_The_Atomic_Nucleus