Glossary
Ammeter
An instrument used to measure the electric current flowing through a point in a circuit, connected in series with the path of the current.
Example:
To measure the total current supplied by a battery, an ammeter must be placed in series with the battery and the rest of the circuit.
Circuit
A closed path or loop through which electrical current can flow continuously.
Example:
A simple flashlight uses a circuit where current flows from the battery, through the bulb, and back to the battery.
Closed Loop
A continuous, unbroken path within a circuit that allows for the flow of electrical current.
Example:
For a light bulb to illuminate, the wires must form a closed loop connecting it to the power source.
Electromotive Force (EMF)
The maximum potential difference a battery or power source can provide when no current is being drawn from it; it represents the total energy per unit charge supplied by the source.
Example:
A 1.5V AA battery has an electromotive force of 1.5 volts, which is its voltage when it's not connected to any load.
Internal Resistance
The inherent resistance within a real voltage source (like a battery) that causes a voltage drop when current flows, reducing the terminal voltage.
Example:
A car battery might have a small internal resistance that causes its voltage to dip slightly when the engine is cranking and drawing a large current.
Kirchhoff's Current Law (KCL)
States that the total current entering a junction (node) in a circuit must equal the total current leaving that junction, reflecting the conservation of charge.
Example:
At a point where a main wire splits into two branches, Kirchhoff's Current Law dictates that the current entering the split must equal the sum of currents in the two branches.
Kirchhoff's Voltage Law (KVL)
States that the algebraic sum of all voltage drops and rises around any closed loop in a circuit must equal zero, reflecting the conservation of energy.
Example:
When analyzing a multi-loop circuit, applying Kirchhoff's Voltage Law helps determine unknown voltages by summing potential changes around each loop.
Open Circuit
A circuit with a break or discontinuity in its path, preventing the flow of electrical current.
Example:
If a switch is flipped to the 'off' position, it creates an open circuit, stopping the flow of electricity to the device.
Parallel Circuit
A circuit configuration where components are connected side-by-side, providing multiple independent paths for current flow.
Example:
Household outlets are wired in a parallel circuit, allowing multiple appliances to operate simultaneously without affecting each other's voltage.
Parallel Resistors
Resistors connected in a parallel configuration, where the reciprocal of their total equivalent resistance is the sum of the reciprocals of their individual resistances.
Example:
Connecting two 10Ω parallel resistors results in a combined resistance of 5Ω, effectively decreasing the overall resistance of the circuit.
Resistivity
An intrinsic material property that quantifies how strongly a given material opposes the flow of electric current, independent of its dimensions.
Example:
Copper has a very low resistivity, which is why it's commonly used for electrical wiring, while rubber has high resistivity, making it an insulator.
Series Circuit
A circuit configuration where components are connected end-to-end, forming a single path for current flow.
Example:
Old Christmas lights were often wired in a series circuit, so if one bulb burned out, the entire string would go dark.
Series Resistors
Resistors connected in a series configuration, where their total equivalent resistance is the sum of their individual resistances.
Example:
If you have two 10Ω series resistors, their combined resistance is 20Ω, increasing the overall opposition to current.
Terminal Voltage
The actual voltage measured across the terminals of a real battery or power source when current is flowing through an external circuit, which is less than the EMF due to internal resistance.
Example:
When a battery powers a device, its terminal voltage will be slightly lower than its EMF because of the voltage drop across its internal resistance.
Voltmeter
An instrument used to measure the potential difference (voltage) between two points in a circuit, connected in parallel with the component being measured.
Example:
To check the voltage across a resistor, you would connect a voltmeter in parallel with it.