Lecture%2028%202220%20Spring%202009

Lecture%2028%202220%20Spring%202009 - Reminders and...

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1 Reminders and Announcements • HW 16 is due today; HW 17 is due next Tuesday; HW 18 is due next Friday • No quiz this week but some of recitation No quiz this week, but some of recitation time will be used for course evaluation. • We will be grading the exams early next week. • Help Room Hours (Physics 117): – M 4-8 pm, T 3-6:30, W 3-6:30, R 4:30-8, F 2-6 Resistors in an AC Circuit • Consider a circuit consisting of an AC source and a resistor • The AC source is symbolized by Δ v = Δ v R = Δ v max sin ω t Δ v R is the instantaneous voltage across the resistor Resistors in an AC Circuit, 2 • The instantaneous current in the resistor is sin sin max max I R R vV i ω t ω t RR ΔΔ == = • The instantaneous voltage across the resistor is also given as Δ v R = I max R sin ω t Phasor Representation rms Current and Voltage • The average current in one cycle is zero • The rms current is the average of importance in an AC circui in an AC circuit • rms stands for root mean square • Alternating voltages can also be discussed in terms of rms values 0707 2 max max I I .I rms 2 max max . rms V VV Δ Δ= = Δ Power • The rate at which electrical energy is dissipated in the circuit is given by P = i 2 R, where i is the instantaneous current • The average power delivered to a resistor that carries an alternating current is 2 I av rms PR =
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2 Notes About rms Values • rms values are used when discussing alternating currents and voltages because – AC ammeters and voltmeters are designed to read rms values – Many of the equations that will be used have the same form as their DC counterparts Which of the following statements might be true for a resistor connected to a sinusoidal AC source? 25% 25% 25% 25% 1. 2. 1234 3. 4. 0 of 126 Inductors in an AC Circuit • Kirchhoff’s loop rule can be applied and gives: 0 o r 0 max , sin L vv di vL dt di V ω t dt Δ+Δ = Δ− = Δ= Current in an Inductor • The equation obtained from Kirchhoff's loop rule can be solved for the current max sin max cos VV i ω td t ω t Δ Δ = =−
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Lecture%2028%202220%20Spring%202009 - Reminders and...

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