Deck 26: Ac Electricity

Question 1

A series AC circuit is shown.The inductor has a reactance of 70 Ω and an inductance of 210 mH.A 40 Ω resistor and a capacitor whose reactance is 70 Ω are also in the circuit.The rms current in the circuit is 1.9 A.In the figure,the capacitance of the capacitor is closest to:

A)43 μF
B)46 μF
C)40 μF
D)37 μF
E)34 μF

Answer 1

43 μF

Question 2

At 3.68100017 kHz the reactance in a circuit of a 9.0 μF capacitor and an inductor are equal in magnitude.What is the value of the inductor?

A)0.00021 μH
B)0.000020 mH
C)0.00021 mH
D)0.000020 H

Answer 2

0.00021 μH

Question 3

A series AC circuit is shown.The inductor has a reactance of 60 Ω and an inductance of 170 mH.A 80 Ω resistor and a capacitor whose reactance is 110 Ω are also in the circuit.The rms current in the circuit is 1.6 A.In the figure,the voltage amplitude across the capacitor is closest to:

A)250 V
B)180 V
C)320 V
D)390 V
E)110 V

Answer 3

250 V

Question 4

The 60 Hz ac source of a series circuit has a voltage amplitude of 120 V.The capacitive and inductive reactances are 980 Ω and 240 Ω,respectively.The resistance is 550 Ω.In the figure,the inductance,in mH,is closest to:

A)640
B)1400
C)2400
D)3000
E)4000

Question 5

An AC source whose rms voltage is 80 V is in series with a 100 Ω resistor and a capacitor whose reactance is 200 Ω at the frequency of the source.In the figure,the rms voltage across the capacitor is closest to:

A)66 V
B)68 V
C)70 V
D)72 V
E)74 V

Question 6

A series RLC circuit has a peak current of 1.0 A with a frequency of 66 kHz.If the resistance of the circuit is 51 kΩ the capacitance of the circuit is 13 μF,and the inductance of the circuit is 30 H,determine the average power of the circuit over one cycle.

A)26,000 W
B)77,000 W
C)7700 W
D)4100 W

Question 7

The inductor in a radio receiver carries a current of amplitude 200 mA when a voltage of amplitude 2.4 V is across it at a frequency of 1400 Hz.What is the value of the inductance?

A)1.43 mH
B)1.36 mH
C)9.20 mH
D)4.42 mH
E)1.97 mH

Question 8

An alternating current is supplied to an electronic component with a rating that it be used only for voltages below 12 V.What is the highest Vrms that can be supplied to this component while staying below the voltage limit?

A)6 V
B)12 V
C)144 V
D)6 V

Question 9

The 60 Hz ac source of a series circuit has a voltage amplitude of 120 V.The capacitive and inductive reactances are 780 Ω and 210 Ω.respectively.The resistance is 460 Ω.In the figure,the rms current in the circuit is closest to:

A)0.12 A
B)0.13 A
C)0.14 A
D)0.16 A
E)0.18 A

Question 10

In a purely resistive AC circuit,when the voltage is at its maximum,the current is at its maximum value as well.

Question 11

A series circuit has a 50 Hz AC source,a 30 Ω resistor,a 0.30 H inductor,and a 50 μF capacitor,as shown.The rms current in the circuit is 1.6 A.In the figure,the voltage amplitude of the source is closest to:

A)97 V
B)83 V
C)69 V
D)56 V
E)48 V

Question 12

The reactance of a capacitor is 7.0 kΩ at a frequency of 0.30 kHz.What is the capacitance?

A)0.076 μF
B)0.48 μF
C)3.0 μF
D)0.107 μF

Question 13

An RLC circuit has a reactance,due to its capacitance,of 11 kΩ;a reactance,due to its inductance,of 3 kΩ;and a resistance of 29 kΩ.What is the power factor of the circuit?

A)0.96
B)0.27
C)1.04
D)0.48

Question 14

A series AC circuit is shown.The inductor has a reactance of 50 Ω and an inductance of 250 mH.A 40 Ω resistor and a capacitor whose reactance is 150 ohms are also in the circuit.The rms current in the circuit is 2.0 A.In the figure,the rms voltage of the source is closest to:

A)220 V
B)180 V
C)150 V
D)110 V
E)80 V

Question 15

An alternating current is supplied to a lightbulb,which strobes.A motor rotates a white fan (with one blade painted red)at 504 Hz in the light from the strobing bulb,and the fan appears to stand still.At 252 Hz the red blade alternates between two positions that are 180° apart.What is the angular frequency of the current? (Be careful,the light will strobe regardless of the sign of the current. )

A)504π rad/s
B)252π rad/s
C)1008π rad/s
D)126π rad/s

Question 16

An LC circuit has a resonance frequency of 9.0 kHz.If the inductor in the circuit has a value of 8.0 H,what is the capacitance of the circuit?

A)0.04 pF
B)39 pF
C)1.5 pF
D)4.4 pF

Question 17

The 60 Hz ac source of a series circuit has a voltage amplitude of 120 V.The capacitive and inductive reactances are 980 Ω and 270 Ω,respectively.The resistance is 550 Ω.In the figure,the capacitance,in μF,is closest to:

A)2.7
B)5.2
C)7.8
D)10
E)16

Question 18

A circuit containing a 39-H inductor has an alternating current supplied to it.If I_rms is 10.0 A and V_p is 18 V,find the frequency of the signal.

A)0.0052 Hz
B)0.21 Hz
C)0.033 Hz
D)0.41 Hz

Question 19

An RLC circuit has a sinusoidal voltage supplied to it at 632 kHz with a peak voltage of 748 V;a 25 kΩ resistance;a 16 μF capacitance;and a 30 H inductance.What is the peak current for this circuit?

A)6.3 μA
B)11 μA
C)26 μA
D)30 μA

Question 20

What is the resonance frequency of an LC circuit consisting of a 26.0 μF capacitor and a 0.010 H inductor?

A)0.31 kHz
B)2.0 kHz
C)3.2 kHz
D)12 kHz

Question 21

The AC current through a capacitor lags the capacitor voltage by 90°.

Question 22

To find the resonant frequency of an RLC circuit,you could adjust the frequency of the AC source until the current reaches its minimum value.

Question 23

In a series RLC circuit,the current is largest at resonance.

Question 24

Power loss in the transmission lines depends linearly on the current.

Question 25

A capacitor,initially having a charge Q on the left plate and a charge -Q on the right plate,is connected to a switch and an inductor,as shown in the figure. Assuming the resistance of the circuit is zero,when the switch is closed,

A)charge will flow out of the capacitor until the left plate is no longer charged,and then all current ceases.
B)current will flow until the left plate of the capacitor has a charge -Q,and then current will flow in the opposite direction,reversing again when the left plate has a charge of +Q.The cycle will then repeat over and over.
C)current will flow through the inductor back and forth,with the magnitude of the current decreasing and eventually going to zero.
D)None of the above

Question 26

Why is it not possible to have an LC circuit oscillate if the frequency of the signal constantly changes?

Question 27

In an AC circuit consisting of a resistor and capacitor in series with each other,the sum of the peak voltages across the resistor and across the capacitor must add up to the emf of the AC source.

Question 28

A capacitor,initially having a charge Q on the left plate and a charge -Q on the right plate,is connected to a switch and an inductor,as shown below.The frequency in which the current will flow back and forth after the switch is closed will increase if

A)the inductance of the inductor is increased.
B)the capacitance of the capacitor is increased.
C)the initial charge of the capacitor is increased.
D)More than one of the above
E)None of the above

Question 29

In an oscillating LC circuit,larger values of L and C give rise to an oscillation with a higher frequency.

Question 30

If a circuit doubles its peak voltage,what happens to its rms voltage?

Question 31

Just as a 100 Ω resistor always has the same resistance no matter what circuit it is in,likewise a 50 μF capacitor always has the same reactance no matter what circuit it is in.

Question 32

A step-up transformer lowers current but raises voltage.

Question 33

For circuits with either an inductor and/or a capacitor,the current gets out of phase with the voltage.For these circuits how are the frequencies of the current and voltage related?

Question 34

A circuit with alternating current has its voltage and current in phase.How does the average power compare to the root mean square of the current and voltage?

Question 35

An LRC circuit is driven by a AC voltage source [where V(t)= Vo sin(ω t)],as shown in the figure.The rate that energy is dissipated by the resistor

A)does not depend on the value of R.
B)will always increase if the angular frequency is increased.
C)will always increase if the angular frequency is decreased.
D)None of the above