Glossary
Ammeter
A measuring instrument used to determine the electric current flowing through a component or part of a circuit.
Example:
To measure the current consumed by a small LED, you would connect an ammeter in series with the LED.
Charge Carriers
Particles, typically electrons in metals or ions in solutions, that are responsible for the flow of electric charge in a material.
Example:
In a typical copper wire, the free electrons act as the primary charge carriers, enabling the flow of electricity.
Charge of Each Carrier (q)
The magnitude of the electric charge carried by a single charge carrier, often the elementary charge (e) for electrons.
Example:
For electrons, the charge of each carrier is approximately 1.6 x 10^-19 Coulombs.
Conservation of Charge
A fundamental principle stating that the total electric charge in an isolated system remains constant; charge cannot be created or destroyed, only transferred.
Example:
In a circuit, electrons move from one component to another, but the total amount of conservation of charge within the entire closed system never changes.
Conventional Current
A historical convention that defines the direction of current as the direction a positive charge would flow, from higher to lower potential, even though electrons (negative charges) are often the actual moving charge carriers.
Example:
When drawing circuit diagrams, we typically indicate the flow of conventional current from the positive terminal of a battery to the negative terminal.
Cross-sectional Area of the Wire (A)
The area of the wire perpendicular to the direction of current flow.
Example:
A thicker extension cord has a larger cross-sectional area of the wire, allowing it to carry more current safely without overheating.
Current (I)
The rate at which electric charge flows past a specific point in a circuit, measured in Amperes (A).
Example:
A high current flowing through a light bulb's filament causes it to glow brightly.
Drift Velocity (vd)
The average velocity of charge carriers in a material due to an electric field, which is typically very slow (on the order of millimeters per second).
Example:
Despite the rapid propagation of electrical signals, the individual electrons in a wire move with a surprisingly slow drift velocity.
Electric Charge
A fundamental property of matter that causes it to experience a force when placed in an electromagnetic field.
Example:
When you rub a balloon on your hair, the balloon gains a net negative electric charge, allowing it to stick to a wall.
Internal Resistance
The inherent resistance within a power source or measuring device that causes a drop in voltage or affects current measurement.
Example:
An ideal ammeter has very low internal resistance to ensure it doesn't significantly alter the current it's measuring.
Number Density of Charge Carriers (n)
The number of free charge carriers per unit volume within a material.
Example:
Metals are excellent conductors because they have a very high number density of charge carriers, meaning many electrons are free to move.
Voltmeter
A measuring instrument used to determine the potential difference (voltage) across two points in a circuit.
Example:
To check the voltage supplied by a battery, you would connect a voltmeter in parallel across its terminals.