NCEA Level 3 Physics - Electrical Systems Vocabulary

A set of vocabulary flashcards defining key electrical concepts, laws, components, and mathematical relationships from the Level 3 Electrical Systems lecture notes.

Conventional Current

The direction defined as the flow of positive charge, which is opposite to the direction of negative electron flow.

Voltage

The energy lost or gained per unit charge between points in an electric field, measured in Volts ($\text{V}$).

Ohm's Law

The relationship stating that current is proportional to applied voltage and limited by resistance, expressed as $V = IR$.

Equivalent Resistance

A single total resistance that represents the combined effect of multiple resistors arranged in series or parallel.

Internal Resistance

The intrinsic resistance within a voltage source that reduces its output terminal voltage when current flows.

Electromotive Force (emf)

The total voltage or energy per unit charge generated by a power source before internal resistance losses occur.

Kirchhoff's Current Law

The rule stating that the total current entering a circuit node must equal the total current leaving that node ($I_{\text{in}} = I_{\text{out}}$).

Kirchhoff's Voltage Law

The rule stating that the algebraic sum of all voltages around any closed circuit loop is equal to zero.

Capacitance

The amount of electric charge stored per volt of applied voltage ($C = \frac{Q}{V}$), measured in Farads ($\text{F}$).

Dielectric

An electric insulating material placed between capacitor plates that allows charge separation within itself to store electric energy and increase capacitance.

Relative Permittivity

A parameter that quantifies the ability of a dielectric material to increase capacitance compared to a vacuum.

Time Constant (\tau)

The time required for a $63\%$ change in voltage, current, or charge during charging or discharging in a capacitive ($\tau = RC$) or inductive ($\tau = \frac{L}{R}$) circuit.

Magnetic Flux

A measure of the total magnetic field passing through a given surface area ($\Phi = BA \cos(\theta)$), measured in Webers ($\text{Wb}$).

Faraday's Law

The law stating that a changing magnetic flux induces an electromotive force (emf) proportional to the rate of change ($\mathcal{E} = -\frac{\Delta \Phi}{\Delta t}$).

Lenz's Law

The principle stating that an induced current always flows in a direction such that its magnetic field opposes the change in magnetic flux that created it.

Self Inductance

A measure of how effectively a conductor induces a back emf in itself when its current changes ($\mathcal{E} = -L \frac{\Delta I}{\Delta t}$), measured in Henrys ($\text{H}$).

Inductor

A circuit component designed to have self-inductance, producing a back emf to oppose sudden changes in current.

Mutual Inductance

The induction of an electromotive force in one coil caused by a changing magnetic flux produced by a nearby coil.

Transformer

A device composed of primary and secondary coils wrapped around a core that uses mutual inductance to step up or step down AC voltage.

Alternating Current (AC)

An electric current that periodically reverses direction, with voltage and current following sinusoidal wave patterns ($V = V_{\text{Max}} \sin(\omega t)$).

Root Mean Square (RMS)

The effective constant value of an alternating voltage or current ($V_{\text{Max}} = \sqrt{2} V_{\text{RMS}}$) that delivers equivalent power to a direct current circuit.

LCR Circuit

A resonant circuit consisting of an inductor, capacitor, and resistor where electrical energy continually oscillates between the electric field of the capacitor and magnetic field of the inductor.

Reactance

The opposition to alternating current caused by capacitance ($X_C = \frac{1}{\omega C}$) or inductance ($X_L = \omega L$), where energy is stored rather than dissipated as heat.

Impedance

The total combined opposition to alternating current in a circuit containing both resistance and reactance ($Z = \sqrt{R^2 + X^2}$).

Resonant Frequency

The specific frequency ($f_0 = \frac{1}{2\pi \sqrt{LC}}$) at which inductive reactance and capacitive reactance are equal and cancel out, resulting in minimum impedance and maximum current.