Glossary
Charge carrier density
The number of mobile charge carriers (e.g., electrons in a conductor) per unit volume within a material.
Example:
Metals have a high charge carrier density, which is why they are excellent electrical conductors compared to insulators.
Charge of each carrier
The fundamental electric charge carried by an individual charge carrier, typically the elementary charge 'e' for electrons.
Example:
In a copper wire, the charge of each carrier is the elementary charge of an electron, approximately -1.602 x 10^-19 Coulombs.
Conventional current
The direction in which positive charges would flow, defined as opposite to the actual flow of electrons in most metallic conductors.
Example:
When analyzing a circuit diagram, we typically draw arrows indicating the direction of conventional current, from positive to negative terminals.
Current density
A vector quantity representing the amount of electric current flowing per unit cross-sectional area, indicating the intensity and direction of current flow at a specific point.
Example:
If a wire narrows, the current density increases in the narrower section, even if the total current remains constant.
Drift velocity
The average velocity attained by charged particles, such as electrons, in a material due to an electric field, resulting in a net current.
Example:
Even though electrons move randomly in a wire, a net drift velocity in one direction creates the electric current.
Electric potential difference (voltage)
The difference in electric potential energy per unit charge between two points in an electric field, which drives the flow of electric charge.
Example:
A battery creates an electric potential difference across a circuit, pushing electrons from the negative terminal to the positive.
Electromotive force (emf)
The energy per unit charge supplied by a source (like a battery or generator) to drive current in a circuit, representing the maximum potential difference the source can provide.
Example:
A 9V battery has an electromotive force of 9 volts, meaning it provides 9 joules of energy for every coulomb of charge that passes through it.
Electrons (as charge carriers)
Subatomic particles with a negative elementary charge that are the primary mobile charge carriers responsible for electric current in most metallic conductors.
Example:
In a typical household wire, it's the electrons that actually move to create the electric current, flowing opposite to the conventional current direction.
Ohm's Law
A fundamental relationship stating that the voltage across a conductor is directly proportional to the current flowing through it, given constant resistance ($V=IR$).
Example:
If you double the voltage across a resistor, Ohm's Law predicts that the current through it will also double, assuming its resistance is constant.
Resistance
A measure of a material's opposition to the flow of electric current, depending on its resistivity, length, and cross-sectional area.
Example:
A long, thin wire will have a higher resistance than a short, thick wire made of the same material.
Resistivity
An intrinsic property of a material that quantifies how strongly it resists the flow of electric current, independent of its shape or size.
Example:
Copper has a very low resistivity, making it an excellent material for electrical wiring, while rubber has a very high resistivity.