Transcript No Slide Title

Chapter 16
Inductive AC Circuits
• Objectives
– After completing this chapter, the student
should be able to:
• Describe the phase relationship between current
and voltage in an inductive AC circuit.
• Determine the inductive reactance in an AC
circuit.
• Explain impedance and its effect on inductive
circuits.
• Describe how an inductor-resistor network can
be used for filtering and phase shifting.
• Explain how low-pass and high-pass inductive
circuits operate.
• Inductance in AC circuits
– Inductors offer opposition to current flow.
• Voltage placed across an inductor creates a
magnetic field.
• When AC voltage changes polarity, it causes the
magnetic field to expand and collapse.
• Voltage is induced in the inductor coil called a
counter-electromotive force (CEMF).
• CEMF
– 180 degrees out of phase with the applied
voltage.
– Opposes the applied voltage.
– Opposition is as effective in reducing current
flow as a resistor.
• Inductive reactance
– The opposition offered to current flow by an
inductor.
– Measured in ohms.
– Depends on its inductance and the frequency of
the applied voltage.
– Expressed by the symbol XL.
• The formula for determining inductive
reactance is:
where:
XL= 2fL
 = pi or 3.14.
f = frequency in hertz.
L = inductance in henries.
• Applications of inductive circuits
– Inductors are widely used in electronics.
• Compete with capacitors for filtering and phase
shift applications.
– Inductors have fewer applications than
capacitors because they are:
• larger.
• heavier.
• more expensive.
• Inductors provide a reactive effect while
still completing a DC circuit path.
• Capacitors provide a reactive effect, but
block the DC elements.
• Inductors and capacitors are sometimes
combined to improve the performance of a
circuit.
• Series RL networks are used as high- and
low-pass filters.
• The frequency above or below the
frequencies passed or attenuated is called
the cut-off frequency.
– Symbol is fco.
– Can be determined by the formula:
R
C
2 fL
where fco = cut-off frequency in hertz.
R = resistance in ohms.
 = 3.14.
f = frequency in hertz.
L = inductance in henries.
• In Summary
– In a pure inductive circuit, the current lags the
applied voltage by 90 degrees.
– Inductive reactance
• the opposition to current flow offered by an
inductor in an AC circuit.
• symbol is XL.
• measured in ohms.
• Formula: XL = 2fL.
• Impedance
• RL circuits used for:
– High-pass filters.
– Low-pass filters.