Electromagnetism

Electric Field

A region around a charged object where other charged objects experience a force.

Electric Potential

The amount of electrical potential energy per unit charge at a point in an electric field.

Electron Volt

A unit of energy equal to the amount of kinetic energy gained by a single electron accelerated through an electric potential difference of one volt.

Charge Separation in Clouds

The process where opposite charges accumulate in different parts of a cloud, creating a strong electric field.

Ionization

The process by which atoms are electrically charged either by gaining or losing electrons.

Lightning Conductor

A device to protect buildings from lightning strikes by directing the electric current safely to the ground.

Electron Avalanche

A rapid multiplication of electrons resulting from ionization, leading to a conductive path in a high electric field.

Breakdown Voltage

The minimum electric field strength required to ionize a medium and create a conductive path.

Potential Difference

The difference in electric potential energy per unit charge between two points in an electric field.

Equipotential Surface / Line

A surface (3D) or line (2D) on which the electric potential is the same at every point, meaning no work is done when moving along it. Perpendicular to field lines at all points.

Charge Quantization

The concept that electric charge is not continuous, but rather exists in discrete amounts, specifically integer multiples of the elementary charge.

Polar Molecule

A molecule that has a charge separation, having a slight positive charge at one end and a slight negative charge at the other.

Insulators

Materials in which electrons are tightly bound to atoms and cannot move freely, such as wood or rubber.

Conductors

Materials that contain electrons that are loosely bound to the atoms, allowing charge to move freely, such as copper and iron.

Charging by Contact

The process of transferring charge through direct physical contact between materials.

Charging by Induction

The process of inducing charges within an object without direct contact, usually involving the influence of a nearby charged object.

Electrical Polarization

The separation of charges within a neutral object when influenced by an external electric field.

Unit of Electric Potential (Volt)

Defined as joule per coulomb (1 V = 1 J/C), representing the potential energy per unit charge.

Source of Electric Potential

Devices like batteries that maintain an electric potential difference between their terminals.

Kinetic Energy In an electric field

The energy an object possesses due to its motion, which increases when a charge moves through an electric field.

Work Done by Electric Field

The energy transferred by the electric field when moving a charge against the electric potential.

Force Field

A vector field that represents the magnitude and direction of forces acting at each point in space.

Electric Field Strength

The force experienced by a positive test charge per unit charge, measured in N/C.

Electric Field Lines

Imaginary lines that represent the direction and strength of an electric field; they start on positive charges and end on negative charges.

Superposition of Electric Fields

The principle that the resultant electric field at a point is the vector sum of the electric fields produced by individual charges.

Faraday Cage

A conductive enclosure that shields its interior from external electric fields.

Test Charge

A small charge used to probe the electric field at a point without affecting the field itself.

Vector Sum of Charges

The total electric field calculated from the individual contributions of multiple charge sources, considering their directions and magnitudes.

Gravitational Force Field

A gravitational field where the force on a mass is uniform, represented by the acceleration due to gravity, approximately 9.8 m/s².

Electric Charge

A physical quantity that can attract or repel other charges, existing in two types: positive and negative.

Charge Conservation

The principle that the net amount of electric charge produced in any process is zero; charge cannot be created or destroyed.

Static Electricity

An imbalance of electric charges within or on the surface of a material, leading to phenomena such as attraction or repulsion.

Coulomb's Law

The law specifying that the electric force between two charges is proportional to the product of the charges and inversely proportional to the square of the distance between them.

Electric Potential (Voltage)

The electric potential energy per unit charge, representing the work done to move a charge against an electric field.

Electric Discharge

A release of electricity, often seen as a visible spark or lightning, typically occurring when an electric field exceeds a critical strength.

Ammeter

A device for measuring the current in a component of a circuit by measuring the current passing through itself.

Ammeter Connection

The device must be connected in series with the component of interest to measure the current passing through it.

Ammeter Resistance

To avoid affecting the quantity it is measuring, its resistance must be very much less than the resistance in the circuit.

Voltmeter

A device for measuring the potential difference across a component of a circuit by measuring the potential difference between its own terminals.

Voltmeter Connection

The device must be connected in parallel with the component of interest.

Voltmeter Resistance

To avoid affecting the quantity it is measuring, its resistance must be very much greater than the resistance of the component.

Electric Shock Severity Factors

The severity depends on the magnitude of the current, the duration of the current flow, and the part of the body the current passes through.

Defibrillation Current

A current of $6000\,mA$ ($6\,A$) which causes sustained ventricular contraction and respiratory paralysis that cease when the shock ends, allowing the heartbeat to return to normal.

Electric circuit

A continuous conducting path between the terminals of a battery through which charges can move.

Electric current ($I$)

The net amount of electric charge ($\Delta Q$) passing the full cross section at some point in a wire per unit time ($\Delta t$ ), defined by the formula $I=\frac{\Delta Q}{\Delta t}$ .

Ampere ($A$)

The unit of current equal to one coulomb per second ($1\,C/s$).

Conventional current

A sign convention where moving charges are considered positive; the flow is opposite to the flow of actual electrons.

Electric shockwave (signal)

A rapidly propagating change in the electric field that moves through a wire close to the speed of light ($\sim 10^8\,m/s$).

Drift speed

The average speed at which actual charges move through a wire, which is approximately $10^{-4}\,m/s$.

Steady current properties

In a circuit with only one conducting path, the current at any instant is the same at every point because charge does not accumulate anywhere.

Direct Current (DC)

The flow of electric charge that moves in only one direction.

Alternating Current (AC)

The flow of electric charge that periodically reverses direction.

AC supply voltage advantage

Household electricity is AC because it is much easier to change the voltage of an AC supply compared to a DC supply.

Peak Voltage ($V_O$)

The maximum voltage value in an AC system, where the voltage varies mathematically between $+V_O$ and $-V_O$ according to the formula $V=V_{o}\text{sin}(2\pi ft)$ .

Average Power ($P_{average}$) in AC

The product of voltage and current over time, expressed as $P_{average} = \frac{1}{2} V_o I_o$ when current and voltage are in phase.

Root Mean Square (rms) Voltage ($V_{RMS}$)

The effective or average voltage value defined as $V_{RMS} = \frac{V_o}{\sqrt{2}}$, which allows AC power formulas to resemble DC formulas.

Root Mean Square (rms) Current ($I_{RMS}$)

The effective or average current value defined as $I_{RMS} = \frac{I_o}{\sqrt{2}}$, used to calculate power transformation in a resistor.

Nominal Australian Domestic Supply

The standard domestic supply which has a $V_{RMS}$ of $240\,V$, corresponding to a peak voltage ($V_o$) of approximately $340\,V$.

AC Average Power Equations

The formulas for power in a resistor using rms values: $P_{average} = V_{rms} I_{rms} = I_{rms}^2 R = \frac{V_{rms}^2}{R}$.

Power Loss in Transmission ($P_{lost}$)

The power dissipated during transmission, calculated using the formula $P_{lost} = I^2 R_{wires}$.

Transmitted Current ($I$)

The current sent through lines, calculated as $I = \frac{P}{V}$; using a high voltage reduces this current to minimize power loss.

Resistance of Wires ($R_{wires}$)

The resistance defined by the property of the materials used, calculated as $R_{wires} = \frac{\rho L}{A}$; it is minimized by using thick wires with low resistivity.

Electric Power

The rate at which electrical energy is transformed into another form of energy, such as thermal energy in a heater or mechanical energy in a motor, defined by the formula $P = \frac{\text{energy transformed}}{\text{time}} = \frac{qV}{\Delta t}$.

$$P = VI$$

The expression for the power transformed in any device, representing the rate of energy transformation when the current passing through it is $I$ and the potential difference between its terminals is $V$.

Watt ($W$)

The unit of electric power, which is equivalent to one Joule per second ($J/s$).

Ohm's Law alternative power expressions

Equivalent expressions for power derived by combining $P = VI$ with $V = IR$ or $I = V/R$, resulting in $P = I^2 R$ and $P = \frac{V^2}{R}$.

kWh (kilo-Watt hour)

A unit of energy rating commonly used for electric devices, representing power multiplied by time.

$1\,kWh$ conversion to Joules

$1\,kWh \times 3600\,\text{seconds} = 3.6 \times 10^6\,\text{Joules}$.

Kirchhoff’s First Rule

Also known as the junction rule, it states that the sum of all currents entering a junction must equal the sum of all currents leaving the junction, which is summarized as $\sum I = 0$ at a junction.

Junction

In a circuit, these are points where three or more wires connect.

Kirchhoff’s Second Rule

Also known as the loop rule, it states that the algebraic sum of changes in potential around any closed circuit path (loop) must be zero ($\sum V = 0$).

Potential Change (Battery, negative to positive)

When the direction of travel is through a battery from the negative terminal to the positive terminal, the change in potential is $\Delta V = +V$.

Potential Change (Battery, positive to negative)

When the direction of travel is through a battery from the positive terminal to the negative terminal, the change in potential is $\Delta V = -V$.

Circuit Analysis Loop Requirement

A problem-solving rule stating that every component must be contained in at least one loop, though a component may be included in more than one. This ensures that Kirchhoff's laws can be applied uniformly across the entire circuit.

Minus Signs in Current Results

In solved circuit equations, a negative value for a current (e.g., $I_3 = -2A$) indicates that the current is flowing in the opposite direction to what was initially drawn.

Series Equivalent Resistance ($R_S$)

The total resistance of resistors connected in series, calculated by the sum of individual resistances: $R_S = R_1 + R_2 + R_3$. Experience the same current.

Parallel Equivalent Resistance ($R_p$)

The total resistance of resistors connected in parallel, calculated using the formula $\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}$ or $R_p = \text{(} \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} \text{)}^{-1}$. Experience the same potential difference.

Electromotive Force (emf)

A source, such as a battery, that creates a potential difference between its terminals to maintain current in a circuit.

Internal Resistance ($r$)

A limitation of nearly all emf sources that causes a potential decrease across the device when a current is drawn.

Terminal Voltage ($V_{terminal}$)

The voltage at the terminals of an emf source when current is flowing, calculated as $V_{terminal} = \text{E} - Ir$. It equals the emf if the current is zero.

Resistance

An inherent property of a material or device, distinct from the current or potential difference applied to it.

Ohm's Law

The principle discovered by Ohm stating that for many materials, resistance at a constant temperature is independent of the potential difference ($V$), often expressed as $V=IR$

Ohmic Resistor

A resistor made of a material where resistance is constant, represented by a straight-line slope on a graph of potential difference ($V$) versus current ($I$).

Non-Ohmic Resistor

A resistor where the resistance is not constant, meaning the slope of potential difference ($V$) versus current ($I$) varies.

Simple Circuit

A closed path for current to flow, consisting of conducting wires connecting a load to the terminals of a battery.

Ideal Battery

A theoretical power source that maintains a constant potential difference ($V$) between its terminals.

Resistivity ($\rho$)

An intrinsic property of a material that relates to its resistance ($R$) through the formula $R = \rho \frac{L}{A}$, and which generally increases as temperature increases.

Ground symbol

The schematic representation used to indicate the zero of potential in a circuit, typically chosen at the negative terminal of the battery.