Glossary
Ammeters
Devices used to measure the electric current flowing through a specific point in a circuit, connected in series with the component being measured.
Example:
An electrician uses an ammeter to check if the correct amount of current is flowing through a household appliance, ensuring it's operating safely.
Electromotive Force (emf, $\mathcal{E}$)
The maximum potential difference a battery or power source can provide when no current is flowing through it; it represents the ideal voltage of the source.
Example:
A 1.5 V AA battery has an electromotive force of 1.5 V, but its terminal voltage might be slightly less when powering a device due to internal resistance.
Equivalent Resistance ($R_{eq}$)
The total resistance of a combination of resistors, representing the single resistance that could replace the group without changing the circuit's total current or voltage.
Example:
To simplify a complex circuit with many resistors, you can calculate the equivalent resistance to treat them as one combined resistor for easier analysis.
Ideal Batteries
Theoretical batteries that provide a constant voltage regardless of the current drawn and possess zero internal resistance.
Example:
In introductory circuit problems, we often assume ideal batteries to simplify calculations, ignoring any voltage drop within the battery itself.
Ideal Wires
Theoretical wires that have zero electrical resistance, meaning they cause no voltage drop and dissipate no power.
Example:
When drawing circuit diagrams, we typically represent connections with ideal wires, implying they perfectly conduct electricity without any energy loss.
Internal Resistance of Batteries ($r$)
The inherent resistance within a real battery that causes a voltage drop across its terminals when current flows, reducing the actual voltage delivered to the external circuit.
Example:
When you start a car, the high current drawn causes a significant voltage drop across the battery's internal resistance, which is why the headlights might dim momentarily.
Non-Ideal Meters
Real-world measuring devices (ammeters or voltmeters) that have internal resistance, causing them to slightly alter the circuit they are measuring.
Example:
Using a non-ideal meter with significant internal resistance can lead to inaccurate readings, as the meter itself draws current or adds resistance to the circuit.
Parallel Connection
A configuration in a circuit where components are connected across the same two points, providing multiple independent paths for current to flow.
Example:
Household electrical outlets are wired in a parallel connection, allowing multiple appliances to receive the same voltage and operate independently.
Resistive Wires
Real-world wires that possess a small but non-zero electrical resistance, which can cause a voltage drop and power dissipation, especially over long distances or with high currents.
Example:
Long extension cords can become warm due to their resistive wires dissipating energy as heat, especially when powering high-current devices.
Series Connection
A configuration in a circuit where components are connected end-to-end, forming a single path for current to flow through each component sequentially.
Example:
When you connect Christmas lights in a series connection, if one bulb goes out, the entire string of lights will turn off because the circuit is broken.
Terminal Voltage ($\Delta V_{ ext{terminal}}$)
The actual potential difference measured across the terminals of a real battery when current is flowing through the external circuit.
Example:
The terminal voltage of a car battery drops significantly when the starter motor is engaged, indicating the effect of its internal resistance.
Voltmeters
Devices used to measure the potential difference (voltage) between two points in a circuit, connected in parallel across the component being measured.
Example:
To verify the voltage supplied to a light bulb, you would connect a voltmeter in parallel across its terminals.