Glossary of Key Terms

Term	Definition	Formula/Unit
Magnetic flux (Φ)	Total magnetic field lines passing through a surface; Φ = BA cos θ	Weber (Wb) = T· $m^{2}$
EMF (electromotive force)	Work done per unit charge; drives current in a circuit	Volt (V)
Faraday's law	EMF induced = negative rate of change of flux	ε = −dΦ/dt
Lenz's law	Induced current direction opposes the change in flux	Direction rule (no formula)
Motional EMF	EMF induced by a conductor moving in a magnetic field	ε = Bvl (V)
Self-inductance (L)	Property opposing change in current through same coil	ε = −L(dI/dt); unit: Henry (H)
Mutual inductance (M)	Coupling coefficient between two coils	ε_{2} = −M(d $I_{1}$ /dt); unit: H
Eddy currents	Induced currents in bulk conductors; cause heating	Reduced by lamination
RMS value	Root mean square; DC-equivalent for power	V_rms = $V_{0}$ /√2
Inductive reactance (X_L)	Opposition of inductor to AC current	X_L = ωL ( $\Omega$ )
Capacitive reactance (X_C)	Opposition of capacitor to AC current	X_C = 1/(ωC) ( $\Omega$ )
Impedance (Z)	Total opposition in AC circuit	Z = √( $R^{2}$ + (X_L−X_C)^{2}) ( $\Omega$ )
Power factor	cos φ; ratio of active to apparent power	cos φ = R/Z
Wattless current	Current component that does no work	I_rms sin φ (A)
Resonant frequency (f_{0})	Frequency at which X_L = X_C	f_{0} = 1/(2π√LC) (Hz)
Q-factor	Sharpness of resonance; voltage magnification	Q = ω_{0}L/R = (1/R)√(L/C)
Transformer	Device changing AC voltage/current via mutual induction	V_s/V_p = N_s/N_p
Turns ratio	Ratio of secondary to primary turns	N_s/N_p
Copper loss	$I^{2}$ R heating in transformer windings	∝ $I^{2}$ (watts)
Hysteresis loss	Energy lost in repeated B-H cycling of core	Reduced by soft iron/silicon steel