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A30.2

A30.2. A current i flows through an inductor L in the direction from point b toward point a . There is zero resistance in the wires of the inductor. If the current is decreasing ,. A. the potential is greater at point a than at point b.

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A30.2

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  1. A30.2 A current i flows through an inductor L in the direction from point b toward point a. There is zero resistance in the wires of the inductor. If the current is decreasing, A. the potential is greater at point a than at point b. B. the potential is less at point a than at point b. C. The answer depends on the magnitude of di/dt compared to the magnitude of i. D. The answer depends on the value of the inductance L. E. both C. and D. are correct.

  2. Chapter 31 Alternating Current Circuits

  3. The left diagram shows the voltage across an AC source as a function of time • On the right is a simple phasor diagram. Phasors and alternating currents

  4. A d’Arsonval galvanometer measures the current through it (see Figures 26.13 and 26.14 below). • Many analog electrical instruments, such as ammeters and voltmeters, use a galvanometer in their design. D’Arsonval galvanometer

  5. To measure alternating current you need something more complicated than a simple analog voltmeter – e.g., a circuit like the one to the right. Root-mean-square values

  6. Ohm’s Law gives the voltage amplitude across a resistor: VR = IR. • Figure 31.7 shows the circuit, the current and voltage as functions of time, and a phasor. Resistor in an ac circuit

  7. The voltage amplitude across the inductor is VL = IXL. • The voltage leads the current by 90◦ Inductor in an ac circuit

  8. The voltage amplitude across the capacitor is VC = IXC • The voltage follows the current by 90◦ Capacitance in an ac circuit

  9. Table 31.1 summarizes the characteristics of a resistor, an inductor, and a capacitor in an ac circuit. • Figure 31.11 (below) shows graphs of resistance and reactance. Comparing ac circuit elements

  10. The woofer (low tones) and the tweeter (high tones) are connected in parallel across the amplifier output. (See Figure 31.12 shown here.) A useful application: the loudspeaker

  11. Q31.1 A resistor is connected across an ac source as shown. For this circuit, what is the relationship between the instantaneous current i through the resistor and the instantaneous voltage vabacross the resistor? A. i is maximum at the same time as vab. B. i is maximum one-quarter cycle before vab. C. i is maximum one-quarter cycle after vab. D. not enough information given to decide

  12. A31.1 A resistor is connected across an ac source as shown. For this circuit, what is the relationship between the instantaneous current i through the resistor and the instantaneous voltage vabacross the resistor? A. i is maximum at the same time as vab. B. i is maximum one-quarter cycle before vab. C. i is maximum one-quarter cycle after vab. D. not enough information given to decide

  13. Q31.2 An inductor is connected across an ac source as shown. For this circuit, what is the relationship between the instantaneous current i through the inductor and the instantaneous voltage vabacross the inductor? A. i is maximum at the same time as vab. B. i is maximum one-quarter cycle before vab. C. i is maximum one-quarter cycle after vab. D. not enough information given to decide

  14. A31.2 An inductor is connected across an ac source as shown. For this circuit, what is the relationship between the instantaneous current i through the inductor and the instantaneous voltage vabacross the inductor? A. i is maximum at the same time as vab. B. i is maximum one-quarter cycle before vab. C. i is maximum one-quarter cycle after vab. D. not enough information given to decide

  15. Q31.3 A capacitor is connected across an ac source as shown. For this circuit, what is the relationship between the instantaneous current i through the capacitor and the instantaneous voltage vabacross the capacitor? A. i is maximum at the same time as vab. B. i is maximum one-quarter cycle before vab. C. i is maximum one-quarter cycle after vab. D. not enough information given to decide

  16. A31.3 A capacitor is connected across an ac source as shown. For this circuit, what is the relationship between the instantaneous current i through the capacitor and the instantaneous voltage vabacross the capacitor? A. i is maximum at the same time as vab. B. i is maximum one-quarter cycle before vab. C. i is maximum one-quarter cycle after vab. D. not enough information given to decide

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