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21-11 LR Circuit

21-11 LR Circuit. Any inductor will have some resistance. An LR circuit has some properties similar to an RC circuit. See formula and diagrams on page 641. See Example 21-12 p 641. 21-12 AC Circuits and Impedance. I=I 0 cos2 p ft …ac current produced. t is time… I 0 is peak current…

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21-11 LR Circuit

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  1. 21-11 LR Circuit • Any inductor will have some resistance. • An LR circuit has some properties similar to an RC circuit. • See formula and diagrams on page 641. • See Example 21-12 p 641.

  2. 21-12 AC Circuits and Impedance I=I0 cos2pft …ac current produced. t is time…I0 is peak current… Vrms =V0 Irms =I0 Resistors…when an ac source is connected to a resistor as in Fig.2—31a, the current increases and decreases with ohm’s law V=IR or I=V/R…current and voltage are in phase…(peaks aligned) P=IV=I2rmsR=V2rms /R

  3. 21-12 AC Circuits and Impedance • Inductor …an inductor, of inductance L , represented by a curly-coil symbol…ignoring the small internal resistance…The voltage applied to the inductor will equal the back emf…(Kirchhoff’s rule of closed circuits) • V-L(DI/Dt)=0 V=L(DI/Dt) • …This equation tell you I is increasing most rapidly when V has its maximum value, V=V0 • I will be decreasing most rapidly when V=-V0 • These 2 instances correspond to points b and d p643 figure 21-32 • Current and voltage are 900 out of phase.

  4. 21-12 AC Circuits and Impedance • …no energy, on average is transformed in an inductor because of this… and no energy is dissipated as thermal energy. • As mentioned in section 21-9, the back emf of an inductor impedes the flow of an ac current. • The magnitude of the current in an inductor is directly proportional to the applied ac voltage at a given frequency. …so • V=IXL …where X is called the inductive reactance or impedance of the inductor….the values can be both rms or peak for both.

  5. 21-12 AC Circuits and Impedance • The constant of proportionality for impedance is 2p, so XL = 2pfL • See Example 21-13 on pg 644. • Capacitors…..when a capacitor is connected to a battery, the capacitor plates quickly acquire equal and opposite charges; but no steady current. • See page 645 figure 21-33 • Current leads the voltage by 900 • This is opposite of an inductor.

  6. 21-12 AC Circuits and Impedance • In an ac circuit, only resistance will dissipate energy by heat. • V=IXC …where X is called the capacitive reactance or impedance of the inductor. • See pg 646 21-13.

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