Sections

Glossary
# Glossary

- back emf
- the emf generated by a running motor, because it consists of a coil turning in a magnetic field; it opposes the voltage powering the motor

- capacitive reactance
- the opposition of a capacitor to a change in current; calculated by ${X}_{C}=\frac{}{}$

- characteristic time constant
- denoted by $\tau \text{,}$ of a particular series
*RL*circuit is calculated by $\tau =\frac{L}{R}\text{,}$ where $L$ is the inductance and $R$ is the resistance

- eddy current
- a current loop in a conductor caused by motional emf

- electric generator
- a device for converting mechanical work into electric energy; it induces an emf by rotating a coil in a magnetic field

- electromagnetic induction
- the process of inducing an emf (voltage) with a change in magnetic flux

- emf induced in a generator coil
- $\text{emf}=\text{NAB}\omega \phantom{\rule{0.25em}{0ex}}\text{sin}\phantom{\rule{0.25em}{0ex}}\mathrm{\omega t}\text{,}$ where $A$ is the area of an $N$-turn coil rotated at a constant angular velocity $\omega $ in a uniform magnetic field $B\text{,}$ over a period of time $t$

- energy stored in an inductor
- self-explanatory; calculated by ${E}_{\text{ind}}=\frac{1}{2}{\text{LI}}^{2}$

- Faraday’s law of induction
- the means of calculating the emf in a coil due to changing magnetic flux, given by $\text{emf}=-N\frac{\mathrm{\Delta \Phi}}{\mathrm{\Delta t}}$

- henry
- the unit of inductance; $1\phantom{\rule{0.25em}{0ex}}\text{H}=1\phantom{\rule{0.25em}{0ex}}\Omega \cdot \text{s}$

- impedance
- the AC analogue to resistance in a DC circuit; it is the combined effect of resistance, inductive reactance, and capacitive reactance in the form $Z=\sqrt{{R}^{2}+({X}_{L}-{X}_{C}{)}^{2}}$

- inductance
- a property of a device describing how efficient it is at inducing emf in another device

- induction
- (magnetic induction) the creation of emfs and hence currents by magnetic fields

- inductive reactance
- the opposition of an inductor to a change in current; calculated by ${X}_{L}=\mathrm{2\pi}\text{fL}$

- inductor
- a device that exhibits significant self-inductance

- Lenz’s law
- the minus sign in Faraday’s law, signifying that the emf induced in a coil opposes the change in magnetic flux

- magnetic damping
- the drag produced by eddy currents

- magnetic flux
- the amount of magnetic field going through a particular area, calculated with $\Phi =\text{BA}\phantom{\rule{0.25em}{0ex}}\text{cos}\phantom{\rule{0.25em}{0ex}}\theta $ where
*$B$*is the magnetic field strength over an area*$A$*at an angle $\theta $ with the perpendicular to the area

- mutual inductance
- how effective a pair of devices are at inducing emfs in each other

- peak emf
- ${\text{emf}}_{0}=\text{NAB}\omega $

- phase angle
- denoted by
*$\varphi \text{,}$*the amount by which the voltage and current are out of phase with each other in a circuit

- power factor
- the amount by which the power delivered in the circuit is less than the theoretical maximum of the circuit due to voltage and current being out of phase; calculated by $\text{cos}\phantom{\rule{0.25em}{0ex}}\varphi $

- resonant frequency
- the frequency at which the impedance in a circuit is at a minimum, and also the frequency at which the circuit would oscillate if not driven by a voltage source; calculated by ${f}_{0}=\frac{1}{\mathrm{2\pi}\sqrt{\text{LC}}}$

- self-inductance
- how effective a device is at inducing emf in itself

- shock hazard
- the term for electrical hazards due to current passing through a human

- step-down transformer
- a transformer that decreases voltage

- step-up transformer
- a transformer that increases voltage

- thermal hazard
- the term for electrical hazards due to overheating

- three-wire system
- the wiring system used at present for safety reasons, with live, neutral, and ground wires

- transformer
- a device that transforms voltages from one value to another using induction

- transformer equation
- the equation showing that the ratio of the secondary to primary voltages in a transformer equals the ratio of the number of loops in their coils; $\frac{{V}_{\text{s}}}{{V}_{\text{p}}}=\frac{{N}_{\text{s}}}{{N}_{\text{p}}}$