1. Chapter 16 Inductive AC Circuits

2. 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.

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

4. 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).

5. 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.

8. 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 X L.

9. The formula for determining inductive reactance is: X L = 2  fL where:  = pi or 3.14. f = frequency in hertz. L = inductance in henries.

10. 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.

11. 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.

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

13. The frequency above or below the frequencies passed or attenuated is called the cut-off frequency. –Symbol is f co. –Can be determined by the formula:

14. where f co = cut-off frequency in hertz. R = resistance in ohms.  = 3.14. f = frequency in hertz. L = inductance in henries.

15. 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 X L. measured in ohms. Formula: X L = 2  fL.

16. Impedance RL circuits used for: –High-pass filters. –Low-pass filters.