Deck 26: Resonance

Question 1

The process of producing sine waves after a pulse of energy has been applied is called ______________ of the LC circuit.

Answer 1

ringing

Question 2

The figure of merit, of the resonant circuit, in sharpness of resonance, is indicated by the factor ______________.

Answer 2

Q

Question 3

The Q is a numerical factor without any units, because it is a ______________ of reactance to resistance and the ohms cancel.

Answer 3

ratio

Question 4

The Q of a resonant circuit can be considered a ______________ factor that determines how much the voltage across L or C is increased by the resonant rise of current in a series circuit.

Question 5

Capacitors used in tuned circuits generally have high Q because of their low ______________.

Question 6

The width of the resonant band of frequencies centered around f_r is called the ______________ of the tuned circuit.

Question 7

The lower the Q, the broader the resonant response and the ______________ the bandwidth.

Question 8

It is simply for convenience in calculations that the bandwidth is defined between the two frequencies having ______________% response.

Question 9

The bandwidth between two frequencies having 70.7% response in current or voltage is also the bandwidth in terms of ______________-power points.

Question 10

______________ means obtaining resonance at different frequencies by varying either L or C.

Question 11

What value of C resonates with a 239-?H L at 1000 kHz?

A) 10.6 pF
B) 106 pF
C) 4184 ?F
D) 418.4 pF

Question 12

What does 4p² equal?

A) 39.48
B) 6.26
C) 9.86
D) 12.56

Question 13

What is used to indicate the quality, or figure of merit of a resonant circuit?

A) ?
B) ?
C) Q
D) ?

Question 14

What is the numerical factor that has no units and is a ratio of reactance to resistance?

A) PF
B) BW
C) Q
D) Z

Question 15

What is the Q of a series circuit that is resonant at 1.0 MHz and develops 50 mV across a 250-?H L with a 2-mV input?

A) 50
B) 25
C) 125
D) 100

Question 16

Capacitors used in tuned circuits generally have high Q because

A) X_C is small
B) X_C­ is large
C) of their low losses
D) inductors have low Qs

Question 17

The width of the resonant band of frequencies centered around f_r is called the

A) bandwidth
B) frequency range
C) half-power points
D) frequency response

Question 18

The group of frequencies with a response of what percentage of maximum, or more, is generally considered the bandwidth of a tuned circuit?

A) 63.7%
B) 70.7%
C) 37.3%
D) 14.1%

Question 19

The lower the Q

A) the more narrow the bandwidth
B) the sharper the resonance
C) the greater the bandwidth
D) the greater the selectivity

Question 20

High Q results in

A) less bandwidth
B) more bandwidth
C) less slope for the skirts of the response curve
D) poor selectivity

Question 21

The frequencies above and below the resonant frequency which have a current or voltage value equal to 70.7% of its value at resonance are called

A) resonant points
B) band points
C) harmonics
D) half-power points

Question 22

Obtaining resonance at different frequencies by varying either L or C is called

A) autoranging
B) AGC
C) tuning
D) calibrating

Question 23

What is a semiconductor device that varies in capacitance when its voltage is changed?

A) Zener diode
B) Tunnel diode
C) Varactor diode
D) Light-emitting diode

Question 24

When a parallel circuit is mistuned

A) it has a high value of impedance
B) current is minimum
C) the LC circuit is not inductive or capacitive
D) it does not have a high value of impedance

Question 25

What is the technique for reducing the Q of a resonant circuit to increase the bandwidth?

A) Attenuating
B) Tuning
C) Damping
D) Limiting

Question 26

The resonance effect occurs

A) when the inductive and capacitive reactances are equal
B) when the inductive and capacitive reactances are unequal
C) when inductance is greater than capacitance
D) regardless of the values of X_L or X_C

Question 27

In radio frequency circuits, the main application of resonance is

A) filtering
B) oscillating
C) tuning
D) coupling

Question 28

Tuning by means of the resonant effect provides a practical application of

A) sensitivity
B) selectivity
C) conductivity
D) resistivity

Question 29

An ac circuit that has equal and opposite reactances is called a(n)

A) resonant circuit
B) resistive circuit
C) resilient circuit
D) reactive circuit

Question 30

The frequency at which the opposite reactances are equal is the

A) oscillating frequency
B) fundamental frequency
C) harmonic frequency
D) resonant frequency

Question 31

What causes the coil resistance to become higher than the coil's dc resistance at higher frequencies?

A) Inductive reactance
B) Capacitive reactance
C) Magnetic effect
D) Skin effect

Question 32

What is the result of plotting frequencies at and near the resonant frequency on a graph?

A) Bode plot
B) Response curve
C) Reactive curve
D) Resonant plot

Question 33

At series resonance, the resonant current is

A) out of phase with the generator voltage
B) in phase with the generator voltage
C) minimum
D) equal to the sum of the individual branch currents

Question 34

At parallel resonance

A) line current is maximum
B) line current is minimum
C) line current is out of phase with the generator voltage
D) impedance is minimum

Question 35

What does 4?² equal?

A) 39.48
B) 6.26
C) 9.86
D) 12.56

Question 36

X_L and X_C can be combined to favor one particular frequency, the resonant frequency to which the LC circuit is tuned.

Question 37

The resonance effect occurs when the inductive and capacitive reactances are equal.

Question 38

Tuning by means of the resonant effect provides a practical application of selectivity.

Question 39

The frequency at which the opposite reactances are equal is the harmonic frequency.

Question 40

The most common application of resonance in rf circuits is called tuning.

Question 41

At higher frequencies, skin effect causes coil resistance to be lower than the coil's dc resistance alone.

Question 42

A response curve of a series resonant circuit shows that current is small below resonance, maximum at resonance, and drops off to small values above resonance.

Question 43

For a series LC circuit at resonance, Z_T = r_s.

Question 44

At resonance the resonant current is in phase with the generator voltage.

Question 45

The advantage of a parallel resonant LC circuit is that Z is minimum only for an ac signal at the resonant frequency.

Question 46

In a parallel resonant circuit, the line current I_T is minimum at the resonant frequency.

Question 47

A parallel LC circuit is often called a tank circuit.

Question 48

Because of the energy stored by L and C, the circulating tank current can provide full sine waves of current and voltage output when the input is only a pulse.

Question 49

Resonant frequency is equal to one divided by the product of two pi times the square root of L times C.

Question 50

A test instrument used to measure inductance or capacitance is the Q meter.