2026-05-17 20:32

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NOTE: $\ast$ means OPTIONAL material to REINFORCE learning

Electrical Charge

Conservation of Change

Before any Elementary discussion of Electromagnetic's happens, it is important to discuss the Law of Conservation of Change.

• $\sum ^{\ast }q=constant$ , essentially ALL charges in a system added remain constant without a external change

Conductors and Insulators $\ast$

Conductors - Electrons can move around freely
Insulator - Electrons CANNOT move around freely

Quick rundown on WHY:
Since like charges repel, in conductors, the electrons move to the edges, while in Insulators, the electrons get STUCK and cannot further move

Charge by Induction $\ast$

Suppose we have two charged rods, where the left one is clearly more negatively charged

Whats interesting, is that if we cut off the wire connecting the affected rod, we actually leave a net positive charge in it permanently.

• This is because as negative charges escape, they have no way of returning to the rod if we cut off the wire, and then remove the rod on the left

Charges

The elementary unit of charge is (e), which is the charge of a single proton. A charge of an electron could be represented as -e
The unit of charges is measured through the coulomb (C).

Unit Conversions

• $C\approx 6.24\cdot {10}^{18}e$
• $e\approx 1.60\cdot {10}^{-19}C$

Coloumbs law $\ast$

Suppose we have two charges at a given distance.
Coulombs Law states:

$F_e$ is the force of electricity, $k_e$ is the proportionality variable, $q_1,q_2$ are charges and $r^2$ is simply distance between them squared

References

4.1 Electric Fields