Inductive AC Circuits

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Chapter 16

• Inductive AC Circuits

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• 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.

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• Describe how an inductor-resistor network can be
  used for filtering and phase shifting.
• Explain how low-pass and high-pass inductive
  circuits operate.

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• 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).

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• 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.

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• 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.

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• The formula for determining inductive reactance
  is
• XL 2?fL
• where ? pi or 3.14.
• f frequency in hertz.
• L inductance in henries.

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• 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.

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• 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.

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• Series RL networks are used as high- and low-pass
  filters.

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• 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

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• where fco cut-off frequency in hertz.
• R resistance in ohms.
• ? 3.14.
• f frequency in hertz.
• L inductance in henries.

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• 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.

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• Impedance
• RL circuits used for
• High-pass filters.
• Low-pass filters.