Introduction to Electric Circuits and Resistance

Flashcards covering the foundational concepts of electric circuits, including basic definitions, units, components, and resistance properties based on the lecture material.

Electric circuit

An interconnection of electrical elements characterized by having a source, a load, a connection from the load to the source, a closed path, and a means to control current flow.

Charge ($Q$ or $q$)

An electrical property of the atomic particles of which matter consists, measured in coulombs ($C$).

Coulomb ($C$)

The unit of electric charge, where $1\,C$ is equivalent to the charge of $6.24 \times 10^{18}$ electrons or protons.

Positive ion

A positive region created by separating a free electron from the basic atomic structure.

Voltage ($V$)

The difference in potential between two points established by creating a separation of positive and negative charges; defined as $V = \frac{W}{Q}$, where $W$ is energy in joules ($J$) and $Q$ is charge in coulombs ($C$).

Current ($I$)

The movement of electric charge defined by the equation $I = \frac{Q}{t}$, where $I$ is in amperes ($A$), $Q$ is in coulombs ($C$), and $t$ is in seconds ($s$).

Ampere ($A$)

The measure of current when $6.242 \times 10^{18}$ electrons ($1\,coulomb$) pass through an imaginary plane in $1\,second$.

Conventional flow

The direction of current flow defined by positive charge movement.

Electron flow

The direction of current flow defined by negative charge movement.

Ampere-hour ($Ah$) rating

A unit of charge for a battery that provides an indication of how long a battery of fixed voltage can supply a particular current, calculated as $\text{Life (hours)} = \frac{\text{ampere-hour rating}}{\text{amperes drawn}}$.

Active element

A circuit element capable of generating energy, such as a voltage source, current source, generator, battery, or amplifier.

Passive element

A circuit element that is not capable of generating energy, such as a resistor, capacitor, or inductor.

Ideal independent source

An active element that provides a specified voltage or current that is completely independent of other circuit elements.

Ideal dependent source

An active element in which the source quantity (voltage or current) is controlled by another voltage or current in the circuit.

Conductors

Materials that permit a generous flow of electrons with very little applied voltage, such as silver, copper, or gold.

Insulators

Materials that have few free electrons and require large applied voltage to establish a measurable current level.

Semiconductors

Materials that exhibit electrical characteristics between those of conductors and those of insulators.

Ammeter

An instrument for measuring current levels that is inserted into the path where the current is to be measured.

Voltmeter

An instrument used for measuring voltages that is connected in parallel to the element being measured.

Power ($P$)

The rate at which work is done or the time rate of change of expending or absorbing energy, defined as $P = \frac{W}{t}$ or $P = VI$ and measured in watts ($W$).

Resistance ($R$)

The property of a material that impedes the flow of current, measured in ohms ($\Omega$).

Mil

A unit of measurement for length related to the inch by the ratio $1000\,mils = 1\,inch$.

Circular mil ($CM$)

A unit of area defined as the area of a wire with a diameter of $1\,mil$, calculated as $A_{CM} = (d_{\text{mils}})^2$.

Positive temperature coefficient

A characteristic of a material where its resistance increases with an increase in temperature.

Negative temperature coefficient

A characteristic of a material where its resistance decreases as temperature increases.

Variable resistors

Resistors in which the values can be changed according to applications, such as potentiometers and rheostats.

Conductance ($G$)

A measure of how well a material conducts electric current, defined as the reciprocal of resistance ($G = \frac{1}{R}$) and measured in siemens ($S$).

Ohmmeter

An instrument for measuring the resistance of a given circuit element; it must never be used in a live circuit.