Deck 13: Rlc Circuits and Resonance

Question 1

Current leads in a series RLC circuitW ith more capacitive reactance than inductive reactance.

Answer 1

True

Question 2

In a resonant circuit, as Q increases the bandwidth decreases.

Answer 2

True

Question 3

To operate the circuit in Figure 13-1 at resonance, ________ the resistance and ________ the frequency.

A)decrease, decrease
B)donʹt change, increase
C)increase, increase
D)donʹt change, decrease

Answer 3

donʹt change, decrease

Question 4

At resonance, X_C equals X_L .

Question 5

If frequency increases in Figure 13-1, the impedance ________ and the current ________.

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

Question 6

The capacitor's resistive effects are significant when considering the Q of an RLC circuit.

Question 7

The total impedance equals the resistance of a resonant series RLC circuit.

Question 8

A series RLC circuit can be configured for band-pass or band-stop filtering purposes.

Question 9

A resonant RLC circuit is said to be very selective if its Q is very low.

Question 10

At resonance, a parallel RLC circuit is inductive.

Question 11

The true power of an RLC circuit depends on the value of resistance.

Question 12

At resonance, a parallel RLC circuit is capacitive.

Question 13

If the resistance increases in Figure 13-1, the impedance ________.

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

Question 14

As the frequency approaches the resonant frequency in Figure 13-1 , the V_R __________

A) becomes increasingly unstable
B) increases
C) remains the same
D) decreases

Question 15

At resonance, a series RLC circuit has maximum current.

Question 16

Find the voltage across the capacitor in Figure 13-1.

A)10.7V
B)0.633V
C)-4.9V
D)5.37V

Question 17

A highly selective filter has a veryW ide bandwidth.

Question 18

At resonance, the impedance of a series RLC circuit equals its resistance.

Question 19

In a series resonant circuit, the impedance is minimum and the current is maximum.

Question 20

In a parallel resonant circuit, the impedance is minimum and the line current is maximum.

Question 21

What is the VOUT/V_IN ratio (expressed in dB) of an RLC series resonant circuit with the output across the inductor if the resonant frequency is 14 MHz, the source voltage is 12 V and the inductor
drops 300 V?

A)13.98 dB
B)25 dB
C)42.91 dB
D)27.96 dB

Question 22

If the current is 0 A in Figure 13-2, maybe ____________

A) the capacitor is shorted
B) the resistor is open
C) the resistor has changed values to 100
D) the inductor is shorted

Question 23

If the resistance increases in Figure 13-2, the bandwidth ________.

A)increases
B)remains the same
C)varies
D)decreases

Question 24

If a resonant circuit has a low Q, it ________.

A)has a smallVoltage across the capacitor
B)has a Wide pass-band
C)tunes sharply
D)has a narrow pass-band

Question 25

If the frequency decreases in Figure 13-1, the impedance ________ and the phase angle ________.

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

Question 26

What is the bandwidth of a resonant circuit if its resonant frequency is 14.2 MHz , the inductive reactance is 3.5 and the coil's resistance is 8 ohm ?

A) 2285 Hz
B) 32.5 kHz
C) 14.2 MHz
D) 28.4 kHz

Question 27

$$\text { Figure } 13 < 2$$

-At resonance, the current in Figure 13-2 is ________.

A)1.66 mA
B)10 A
C)1.66 4
D)10 mA

Question 28

If the resistance decreases in Figure 13-2, the bandwidth ________.

A)decreases
B)varies
C)remains the same
D)increases

Question 29

If the frequency decreases in Figure 13-1, the impedance initally ________ and the current initially ________.

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

Question 30

To operate the circuit in Figure 13-1 below the resonant frequency, ________ the resistance and ________ the frequency.

A)do not change, decrease
B)do not change, increase
C)decrease, decrease
D)increase, increase

Question 31

What is the resonant frequency of a tank circuit with a 50 mH inductor and C=256 pF capacitor?

A) 44.5 kHz
B) 44.5 Hz
C) 445 kHz
D) 4.45 kHz

Question 32

If an LC tank circuit is operating below resonance, the circuit is ________ in nature.

A)inductive
B)capacitive
C)positive
D)resistive

Question 33

If a tuned tank circuit has a very narrow bandwidth, its is probably_________

A) very low
B) below 10
C) about 10
D) very high

Question 34

In a parallel resonant RLC circuit, the impedance is ________ and the total current is ________.

A)maximum. maximum
B)minimum, minimum
C)minimum, maximum
D)maximum, minimum

Question 35

What is the power at f₁ and f₂ in a resonant circuit that delivers 120 W ?

A) 84.8 W at f₁ and 60 W at f₂
B) 84.8 W
C) 60 W
D) 17 W at both frequencies

Question 36

If the resistance decreases in Figure 13-1, the impedance ________.

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

Question 37

If the resistor shorts in Figure 13-2, the current ________.

A)increases
B)continues, but the circuit Would not be resonant
C)decreases
D)does not change

Question 38

What is the current in a parallel RLC circuit if its impedance is 0.22 is 100 and V_S =50 V?

A) 2.27 mA
B) 0.0227 mA
C) 22.7 mA
D) 0.227 mA

Question 39

If the capacitor opens in Figure 13-2, the current ________.

A)remains the same
B)increases because of the inductor
C)continues to flow, but the circuitW
Ould not be resonant
D)decreases to zero

Question 40

The resonant frequency of a tank circuitW ith a 0.150 mH inductor and 300 pF capacitor is ________.

A)1.65 MHz
B)750 kHz
C)6.05 MHz
D)347 kHz

Question 41

What is the bandwidth of the resonant circuit if the resonant frequency is 1.42 MHz , the inductive reactance is 3.5 and the coil's resistance is 8 ohm ?

A) 32.5 kHz
B) 3.25 kHz
C) 1.42 MHz
D) 2285 Hz

Question 42

What is the ratio of (expressed in dB ) in an RLC series resonant circuit if the output voltage is taken across the inductor, the resonant frequency is 14 MHz , the source voltage is 18 V and the inductor drops 300 V ?

A) 28 dB
B) 24.4 dB
C) 14.0 dB
D) 42.9 dB

Question 43

In an ideal parallel resonant circuit, the total current into the L and C branches is ________.

A)high
B)zero
C)low
D)maximum

Question 44

In a series RLC circuit just below the resonant frequency, the impedance is:

A) more inductive.
B) at maximum.
C) more capacitive.
D) at minimum.

Question 45

What is the resonant frequency of a tank circuit with a 150 mH inductor and a 300 pF capacitor?

A) 23.7 kHz
B) 237 kHz
C) 23.7 Hz
D) 2.37 MHz

Question 46

Replacing the inductor in a series resonant band-pass filter with one having a lower $Q$ value causes the bandwidth to_________

A) increase
B) remain the same
C) be more selective
D) decrease

Question 47

What is the source voltage in a series resonant circuit if =150 V, =150 V and =50 V ?

A) 300 V
B) 50 V
C) 350 V
D) 150 V

Question 48

A resonant circuit with a high Q ????????????????????.

A)has aVery Wide pass-band
B)has no pass-band
C)tunes sharply
D)has a small Voltage across the capacitor

Question 49

What is the total current in a parallel resonant circuit if its impedance is 0.22 , the is 100 and the source voltage is 100V?

A) 4.55 mA
B) 0.0455 mA
C) 45.5 mA
D) 0.455 mA

Question 50

If a tank circuit is operating above resonance, it is ______in nature.

A) inductive
B) positive
C) capacitive
D) resistive

Question 51

If the resonant frequency is 1MHz and $Q$ =50, f1= ________ and f2= ________

A) 0.98 MHz, 1.01 MHz
B) 0.98 MHz, 1.02 MHz
C) 0.99 MHz, 1.02MHz
D) 0.99 MHz, 1.01 MHz

Question 52

The total reactance of a series RLC circuit at resonance is ________.

A)infinity
B)equal to the resistance
C)capacitive
D)zero

Question 53

In a series RLC circuit at resonance, the capacitive reactance X_C and the inductive reactance X_L

A) add to each other.
B) cancel each other.
C) are minimum.
D) are moderate.

Question 54

In a parallel RLC circuit,at resonance the capacitive reactance X_C and the inductive reactance X_L :

A) are moderate.
B) equal and oppose current flow.
C) are minimum.
D) add to each to cancel current flow.

Question 55

If a tuned tank circuit has a very wide bandwidth, its $Q$ might be_______

A) about 10
B) about 100
C) very high
D) very low

Question 56

What is the lower cut off frequency in an RLC resonant circuit if the inductive reactance is 1.2 the resonant frequency is 22 kHz and the resistance is 60 ?

A) 21.7 kHz
B) 21.8 kHz
C) 21.5 kHz
D) 20.9 kHz

Question 57

What is the resonant impedance of a series RLC circuit with a 15 mH inductor, 0.015 $\mu \mathrm { F }$ capacitor and 80 $\Omega$ resistor?

A) 30 $\Omega$
B) 15 $\mathrm { k } \Omega$
C) 80 $\Omega$
D) 0 $\Omega$

Question 58

What is the power at f₁ and f₂ in a resonant circuit that delivers 750 W ?

A) 375 W at both frequencies
B) 750 W at both frequencies
C) 375 W at f₁ and 750 W at f₂
D) 17 W at both frequencies

Question 59

In a series RLC circuit at resonance:

A) the impedance is mostly resistive.
B) X_C equals X_L and they cancel.
C) the impedance Z is at minimum.
D) all of these.

Question 60

In a series RLC circuit just above the resonant frequency, the impedance is:

A)more inductive.
B)more capacitive.
C)at maximum.
D)at minimum.

Question 61

Which statement best describes the phase angle of a parallel RLC circuit at resonance?

A)With a net reactance at maximum the phase angle is zero.
B)With a net reactance at minimum the phase angle is zero.
C)Total current flow is minimum.
D)either A or C

Question 62

In a parallel RLC just below the resonant frequency, the impedance is:

A) more capacitive.
B) at maximum.
C) more inductive.
D) at minimum.

Question 63

In a parallel RLC circuit just above the resonant frequency, the impedance is:

A)at minimum.
B)at maximum.
C)more capacitive.
D)more inductive.

Question 64

Why does a resistive load increase the bandwidth of a given band-pass filter?

A)A resistive load actually decreases the bandwidth.
B)The resistance decreases the quality of the circuit.
C)The resistance increases the quality of the circuit.
D)not enough information

Question 65

When tuning across the resonant frequency of a series RLC band-pass filter,W hich of the following is true?

A)The impedance of the filter should be minimum at resonance.
B)Current flow through the load is minimum.
C)The outputVoltage across the load is minimum.
D)The impedance of the filter should be maximum at resonance.

Question 66

The selectivity of a given band-pass filter has degraded significantly, yet the fr isW ithin tolerance. Which of the following could have caused this?

A)The inductance has increased.
B)The load has opened.
C)The capacitance has increased.
D)none of the above

Question 67

Between the lower and upper critical frequencies of a band-pass filter:

A)the frequencies pass a maximum level.
B)the frequencies pass at 70% to their maximum levels.
C)the frequencies pass a minimum level.
D)the frequencies pass at 30% to their maximum levels.

Question 68

The output voltage of a circuit at 70.7% of its maximum level measured in dB is:

A)-3 dB.
B)-7 db.
C)7 dB.
D)3 dB.