Chapter 21 Alternating Current Circuits and Electromagnetic Waves CHAPTER 21 Conceptual Questions C1 In an RLC circuit the maximum current is 1 amp What is the average current a 2 A b 1 2 A c 1 2 A d None of the above C2 In an RC circuit which of the following is a possible phase angle a 45 b 45 c 135 d 135 C3 In a 60 Hz RLC circuit the phase angle is positive The values of the resistance inductance and the capacitance are now doubled Which of the following is now true about the phase angle a It is still positive b It could be zero c It will be negative d It could be positive negative or zero but it cannot be greater than its original value C4 A monochromatic light wave in vacuum has frequency f0 and wavelength 0 Which of the following are also possible frequency and wavelength combinations for a monochromatic light wave in vacuum C a 2f0 2 0 b f0 2 0 2 c 2f0 0 2 d None of the above are possible C5 An RLC circuit has resistance R0 inductance L0 and capacitance C0 If the resistance value is now doubled which values of inductance and capacitance will result in the same resonant frequency as before C a 2L0 2C0 b L0 2 C0 2 c 2L0 C0 2 d 2L0 C0 103 Chapter 21 Alternating Current Circuits and Electromagnetic Waves 21 1 Resistors in an AC Circuit 1 What is the effective rms current value for an AC current with an amplitude of 10 A a 28 A b 3 1 A c 7 1 A d 14 A 2 In an AC series circuit the current in a pure resistor differs in phase with the applied voltage by what angle a zero b 45 c 90 d 180 3 The rate of heat dissipation in an AC circuit with resistance R and effective current Irms is given by which of the following a 0 5 Irms 2R b Irms 2R c 2 0 Irms 2R d 4 0 Irms 2R 4 An AC voltage source with a peak output of 200 V is connected to a 50 resistor What is the effective or rms current in the circuit a 2 8 A b 4 0 A c 5 6 A d 2 0 A 5 An AC voltage source with a peak output of 200 V is connected to a 50 resistor What is the rate of energy dissipated due to heat in the resistor a 200 W b 400 W c 566 W d 800 W 104 Chapter 21 Alternating Current Circuits and Electromagnetic Waves 6 The rms current is equal to the direct current that a produces the same average voltage across a resistor as in an AC circuit b dissipates an equal amount of energy in a resistor at the same rate as in an AC circuit c provides the same average current in a resistor as in an AC circuit d results in the same peak power in a resistor as in an AC circuit 7 An AC voltage source with a peak output of 120 V results in dissipation of energy in a resistor at rate of 100 W What is the value of the resistance a 144 b 120 c 100 d 72 8 The peak voltage of an AC source is 200 V What is the rms voltage a 282 V b 200 V c 141 V d 100 V 9 In the typical household AC voltage of 120 V what is the peak voltage a 240 V b 170 V c 120 V d 85 V 21 2 Capacitors in an AC Circuit 10 The frequency in an AC series circuit is doubled By what factor does this change the capacitive reactance a 1 2 b 1 4 c 2 d 4 11 In an AC series circuit the capacitive reactance is 200 and frequency is 100 Hz What is the capacitance a 3 2 F 105 Chapter 21 Alternating Current Circuits and Electromagnetic Waves b 6 28 F c 8 0 F d 50 0 F 106 Chapter 21 Alternating Current Circuits and Electromagnetic Waves 12 A 12 0 F capacitor is connected to an AC source with an rms voltage of 120 V and a frequency of 60 0 Hz What is the rms current in the capacitor a 1 41 A b 0 768 A c 0 543 A d 0 A 13 When a 50 F capacitor is attached to an AC source its capacitive reactance is 40 If instead a 100 F capacitor is attached to the same source what will be its capacitive reactance a 80 b 57 c 28 d 20 14 In a capacitor in an AC circuit the voltage a leads the current by 90 b lags the current by 90 c may lead or lag the current depending on the frequency d is in phase with 70 7 of the current 21 3 Inductors in an AC Circuit 15 In the inductor of a 60 Hz AC series circuit the peak voltage precedes the peak current in each cycle by what time interval a 2 1 10 3 s b 4 2 10 3 s c 8 3 10 3 s d 1 7 10 3 s 16 In an AC series circuit the voltage in the inductor differs in phase with the voltage in the capacitor by what angle a zero b 45 c 90 d 180 107 Chapter 21 Alternating Current Circuits and Electromagnetic Waves 17 In an AC series circuit the inductive reactance is 50 and the frequency is 100 Hz What is the inductance in the circuit a 80 mH b 240 mH c 500 mH d 740 mH 18 The current in an inductor connected to an AC voltage source lags the voltage This lag is caused by the a back emf in the coil b voltage across the coil c time required for electrical signals to travel through all the coils of an inductance d resistance of the coil 21 4 The RLC Series Circuit 19 What is the impedance of an AC series circuit that is constructed of a 10 0 resistor along with 12 0 inductive reactance and 7 0 capacitive reactance a 37 0 b 27 7 c 27 1 d 11 2 20 What is the phase angle of an AC series circuit that is constructed of a 10 0 resistor along with 12 00 inductive reactance and 7 00 capacitive reactance a 26 6 b 18 4 c 87 0 d 63 4 21 An AC series circuit has 12 0 resistance 15 00 inductive reactance and 10 00 capacitive reactance If an effective rms emf of 120 V is applied what is the effective rms current value a 5 31 A b 9 23 A c 10 8 A d 26 0 A 108 Chapter 21 Alternating Current Circuits and Electromagnetic Waves 22 Consider an AC series circuit containing a coil capacitor and resistance Tripling the frequency will change the inductive reactance by what factor …