Deck 12: Rlcircuits

Question 1

An ohmmeter can be used to accurately test the impedance of an RL circuit.

Answer 1

False

Question 2

If the frequency is 60 Hz in Figure 12 -1, what is the inductance?

A)3.77 H
B)3.77 mH
C)26.5 mH
D)265 mH

Answer 2

265 mH

Question 3

If the frequency increases in an RL circuit, the impedance decreases.

Answer 3

False

Question 4

The impedance of a series RL circuit is found by directly adding the values of XL and R.

Question 5

The impedance of a series RL circuit is found by adding the values of XL and R using a phasor diagram.

Question 6

A low -pass filter passes high frequencies and blocks other frequencies.

Question 7

A high -pass filter passes high frequencies and blocks low frequencies.

Question 8

If the frequency increases in Figure 12 -1, the current .

A)decreases
B)increases
C)remains the same
D)decreases to zero

Question 9

The impedance of an RL series circuit varies inversely with the frequency.

Question 10

The source voltage always lags the total current in an RL circuit.

Question 11

Power dissipated by the resistor in a parallel RL circuit can be increased with the addition of a capacitor in parallel.

Question 12

If the resistance decreases in an RL filter circuit, the cutoff frequency increases.

Question 13

The output at the cutoff frequency of a low pass RL filter is 0 V.

Question 14

If the inductance increases in an RL filter circuit, the cutoff frequency increases.

Question 15

The overall phase angle of a parallel circuit with a resistance of 20 Ω and an inductive reactance of 25 kΩ would be nearly 90 degrees.

Question 16

What is the impedance in Figure 12 -1?

A)1120 Ω
B)104 Ω
C)1040 Ω
D)112 Ω

Question 17

Calculate the true power in Figure 12 -1.

A)400 mW
B)1 W
C)10 W
D)4 W

Question 18

If the frequency increases in Figure 12 -1, the phase angle _.

A)remains the same
B)decreases
C)changes to another quadrant
D)increases

Question 19

The source voltage always leads the total current in an RL circuit.

Question 20

If the frequency increases in Figure 12 -1, inductance .

A)increases
B)decreases to zero
C)remains the same
D)decreases

Question 21

Which statement describes the relationship of IL and IR in Figure 12 -2?

A)IL lags IR.
B)They are 180° out of phase.
C)IL leads IR.
D)They are in phase.

Question 22

What is the apparent power in Figure 12 -1?

A)0.4 VA
B)22.27 VA
C)8.94 VA
D)0.8 VA

Question 23

If the operating frequency decreases in Figure 12 -1, the current .

A)increases
B)remains the same
C)decreases
D)decreases to zero

Question 24

What change would decrease the power factor in Figure 12 -2?

A)Decrease the value of the resistor.
B)Decrease the source voltage.
C)Increase the value of the resistor.
D)Increase the source voltage.

Question 25

If the operating frequency decreases in Figure 12 -1, the inductance .

A)decreases to zero
B)increases
C)remains the same
D)decreases

Question 26

If the source voltage changes to 100 V in Figure 12 -1, the true power is .

A)16 W
B)4 W
C)40 W
D)40 mW

Question 27

What is the total impedance in Figure 12 -2?

A)5.71 kΩ
B)1.86 kΩ
C)9.09 kΩ
D)1.07 kΩ

Question 28

What is the phase angle in Figure 12 -1?

A)71.2°
B)86.3°
C)63.4°
D)54.3°

Question 29

If the frequency decreases in Figure 12 -1, the phase angle and the impedance _.

A)increases, decreases
B)decreases, increases
C)increases, increases
D)decreases, decreases

Question 30

What is the cutoff frequency in Figure 12 -1?

A)30 Hz
B)63 Hz
C)408 Hz
D)25 Hz

Question 31

If the frequency is 400 Hz in Figure 12 -1, what is the inductance?

A)39.8 mH
B)25.1 mH
C)25.12 H
D)39.8 H

Question 32

If the frequency increases in Figure 12 -1, the phase angle and the current _.

A)decreases, increases
B)decreases, decreases
C)increases, increases
D)increases, decreases

Question 33

If the resistance increased to 10 kΩ in Figure 12 -2, the total impedance is .

A)6.61 kΩ
B)13.2 kΩ
C)3.30 kΩ
D)infinite Ω

Question 34

If the resistor decreases in Figure 12 -2, the total current _ _.

A)decreases to zero
B)remains the same
C)increases
D)decreases

Question 35

If the frequency increases in Figure 12 -1, the phase angle and the impedance _.

A)increases, decreases
B)decreases, increases
C)increases, increases
D)decreases, decreases

Question 36

If the operating frequency decreases in Figure 12 -1, the phase angle _.

A)decreases
B)remains the same
C)increases
D)changes to another quadrant

Question 37

What change would increase the power factor in Figure 12 -2?

A)increasing the source voltage
B)decreasing the value of the resistor
C)decreasing the source voltage
D)increasing the value of the resistor

Question 38

What is the voltage across the inductor in Figure 12 -1?

A)0.4 V
B)4.47 V
C)44.6 V
D)0.894 V

Question 39

If the frequency decreases in Figure 12 -1, the phase angle and the current _.

A)increases, increases
B)decreases, decreases
C)decreases, increases
D)increases, decreases

Question 40

If the resistance increases in Figure 12 -2, the total current _ _.

A)increases
B)remains the same
C)decreases
D)decreases to zero

Question 41

When an ac voltage is supplied to an RL circuit, the ac's current and amplitude will be:

A)lagging the voltage.
B)similar in waveform.
C)varying in the same manner.
D)all of these.

Question 42

What is the phase angle in Figure 12 -3, at the cutoff frequency?

A)51.4°
B)54.3°
C)49.9°
D)45.0°

Question 43

The circuit in Figure 12 -3 is known as a filter.

A)high -pass
B)band -pass
C)notch
D)low -pass

Question 44

If some of the turns of the inductor in Figure 12 -3 have shorted, how will the circuit change?

A)The cutoff frequency will increase.
B)The output voltage at the cutoff frequency will decrease.
C)The output voltage at the cutoff frequency will increase.
D)The cutoff frequency will decrease.

Question 45

If the resistive current is 2 A and the inductive current is 2 A in a parallel RL circuit, total current is .

A)4 A
B)2 A
C)5.66 A
D)2.83 A

Question 46

If a load is purely inductive and the reactive power is 10 VAR, the apparent power is .

A)14.14 VA
B)3.16 VA
C)10 VA
D)1.144 VA

Question 47

An RL lag network is similar to a

A)high pass filter.
B)low pass filter.
C)band pass filter.
D)stop pass filter.

Question 48

In a RL circuit, the inductive reactance is:

A)increases as the frequency increases.
B)directly proportional to the frequency.
C)directly proportional to the inductance.
D)all of these.

Question 49

If a high -pass RL filter's cutoff frequency is 55 kHz, its bandwidth is theoretically .

A)110 kHz
B)0 kHz
C)55 kHz
D)infinite

Question 50

If VR is 10 V and VL is 10 V in a series RL circuit, the source voltage equals .

A)14.1 V
B)20 V
C)10 V
D)28.3 V

Question 51

If a low -pass RL filter's cutoff frequency is 20 kHz, its bandwidth is .

A)20 kHz
B)0 Hz
C)40 kHz
D)unknown

Question 52

If the output is taken across the inductor in Figure 12 -3, the circuit is known as a _.

A)low -pass filter
B)band -pass filter
C)high -pass filter
D)notch filter

Question 53

What is the cutoff frequency in Figure 12 -3?

A)796 Hz
B)637 kHz
C)637 Hz
D)7.96 kHz

Question 54

In an RL filter circuit, the cutoff frequency is defined as the frequency at which:

A)the output voltage is cutoff, with minimum or zero output.
B)the output voltage drops to 33% of maximum.
C)the output voltage drops to 66% of maximum.
D)the output voltage drops to 70% of maximum.

Question 55

What is VOUT at the cutoff frequency in Figure 12 -3?

A)15.6 V
B)15.1 V
C)14.4 V
D)12.9 V

Question 56

If the true power is 10 W and the reactive power is 10 VAR, the apparent power is .

A)5 VAT
B)14.1 VA
C)100 VA
D)20 VA

Question 57

Power in an RL circuit can be measured as:

A)apparent power (Pa).
B)true power (Ptrue).
C)reactive power (Pr).
D)all of these.

Question 58

An RL high pass filter takes its output across:

A)the series inductor.
B)the parallel resistor.
C)the parallel inductor.
D)the series resistor.

Question 59

What effect will an open inductor have on the circuit in Figure 12 -3?

A)The output voltage at the cutoff frequency will increase.
B)The current will drop to zero.
C)The cutoff frequency will increase.
D)The output voltage at the cutoff frequency will decrease.

Question 60

In a series RL circuit, as the phase angle between the applied voltage and the total current increases, this is the same as:

A)power factor decreasing.
B)apparent power decreasing.
C)power factor increasing.
D)true power decreasing.

Question 61

A measured voltage of 0 V across the resistor in a parallel RL circuit would indicate:

A)an short in the inductor.
B)a blown fuse.
C)an open in the resistor.
D)either A or B.

Question 62

Which of the following is typically most important of the three types of power in terms of work being done?

A)inductive
B)apparent
C)true
D)reactive

Question 63

In a basic crossover network, there will be a(n) in
With the woofer and a(n)
In _ with the tweeter.

A)capacitor, series, inductor, parallel
B)inductor, series, capacitor, series
C)capacitor, series, inductor, series
D)inductor, parallel, capacitor, series

Question 64

The startup current for large induction motors is very high because

A)the starting impedance is slightly capacitive
B)the power factor is low
C)the counter emf is very high
D)the starting impedance is purely inductive

Question 65

The voltage measured across the inductor in a series RL has dropped significantly from normal. What could possibly be the problem?

A)partial shorting of the windings of the inductor
B)The resistor has gone up in value.
C)The resistor has gone down in value.
D)either A or B

Question 66

After troubleshooting a series RL circuit, you check the resistance of the inductor and it is around 40 ohms. What conclusion does this bring you to?

A)Since the inductor's voltage was nearly zero, the inductor is probably okay, so the resistor must be open.
B)Since the inductor's voltage was nearly zero, the inductor is probably okay so the resistor must be shorted.
C)Since the inductor's voltage was nearly zero, you are sure the windings have shorted.
D)not enough information

Question 67

It is suspected that a high pass filter's cutoff frequency has changed. What pieces of test equipment could be used to check it out?

A)voltmeter and a sine wave generator
B)an oscilloscope and a square wave generator
C)either A or B
D)none of the above