In a sine-wave ac circuit, the current through an inductance lags 90° behind the voltage across the inductance because vL = L(di/dt). This fundamental fact is the basis of all the following relations.
Therefore, inductive reactance XL is a phasor quantity 90° out of phase with R. The phasor combination of XL and R is their impedance ZT.
These three types of opposition to current are compared in Table 21–4.
The phase angle Ø is the angle between the applied voltage and its current.
The opposite characteristics for series and parallel circuits with XL and R are summarized in Table 21–5.
The Q of a coil is XL/ri, where ri is the coil's internal resistance.
A choke is an inductance with XL greater than the series R by a factor of 10 or more.
In sine-wave circuits, VL = IXL. Then VL is out of phase with I by an angle of 90°.
For a circuit with XL and R in series, tan θ = XL/R. When the components are in parallel, tan θ = –(IL/IR). See Table 21–5.
When the current is not a sine wave, vL = L(di/dt). Then the waveshape of VL is different from the waveshape of I.
Inductors are available as surface-mount components. Surface-mount inductors are available in both completely encased and open body styles.
