Deck 13: Rlccircuits and Resonance

Question 1

At resonance, XC equals XL.

Answer 1

True

Question 2

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

Answer 2

False

Question 3

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

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

Answer 3

increases

Question 4

As the frequency approaches the resonant frequency in Figure 13 -1, the VR .

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

Question 5

A highly selective filter has a very wide bandwidth.

Question 6

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

Question 7

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

Question 8

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

Question 9

Current leads in a series RLC circuit with more capacitive reactance than inductive reactance.

Question 10

At resonance, a parallel RLC circuit is capacitive.

Question 11

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

Question 12

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

Question 13

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

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

Question 14

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

Question 15

At resonance, a parallel RLC circuit is inductive.

Question 16

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

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

Question 17

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

Question 18

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

Question 19

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

A)increase, increase
B)don't change, decrease
C)don't change, increase
D)decrease, decrease

Question 20

At resonance, a series RLC circuit has maximum current.

Question 21

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

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

Question 22

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

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

Question 23

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

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

Question 24

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

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

Question 25

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

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

Question 26

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

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

Question 27

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

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

Question 28

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

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

Question 29

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

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

Question 30

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

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

Question 31

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

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

Question 32

What is the VOUT/VIN 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)42.91 dB
B)13.98 dB
C)25 dB
D)27.96 dB

Question 33

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

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

Question 34

If a tuned tank circuit has a very narrow bandwidth, its Q is probably .

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

Question 35

What is the current in a parallel RLC circuit if its impedance is 0.22 MΩ, Q is 100 and VS = 50 V?

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

Question 36

The resonant frequency of a tank circuit with a 0.150 mH inductor and 300 pF capacitor is .

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

Question 37

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

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

Question 38

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

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

Question 39

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

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

Question 40

If a resonant circuit has a low Q, it .

A)has a small voltage across the capacitor
B)has a narrow pass -band
C)tunes sharply
D)has a wide pass -band

Question 41

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

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

Question 42

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

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

Question 43

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

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

Question 44

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

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

Question 45

In a series RLC circuit at resonance, the capacitive reactance (XC)and the inductive reactance (XL):

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

Question 46

What is the ratio of VOUT/VIN (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)14.0 dB
B)24.4 dB
C)28 dB
D)42.9 dB

Question 47

In a parallel RLC circuit,at resonance the capacitive reactance (XC)and the inductive reactance (XL):

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

Question 48

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

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

Question 49

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

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

Question 50

A resonant circuit with a high Q _.

A)has a very wide pass -band
B)has no pass -band
C)tunes sharply
D)has a small voltage across the capacitor

Question 51

In a series RLC circuit at resonance:

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

Question 52

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

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

Question 53

If a tuned tank circuit has a very wide bandwidth, its Q might be .

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

Question 54

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

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

Question 55

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

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

Question 56

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)2.37 MHz
D)23.7 Hz

Question 57

What is the resonant impedance of a series RLC circuit with a 15 mH inductor, 0.015 µF capacitor and 80 Ω resistor?

A)15 kΩ
B)30 Ω
C)80 Ω
D)0 Ω

Question 58

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

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

Question 59

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

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

Question 60

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

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

Question 61

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

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

Question 62

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

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

Question 63

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

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

Question 64

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

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

Question 65

For the tuning circuit of a radio frequency receiver, the filter:

A)high Q components are not necessary.
B)bandwidth should be narrow.
C)need not be highly selective.
D)any of the above

Question 66

A resonant circuit designed to reduce the interference from a specific source is called a

A)shunt conductor
B)break filter
C)wave trap
D)dropout filter

Question 67

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

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

Question 68

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

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

Question 69

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 70

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

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