Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

ELEX > AC Circuit > Flashcards

AC Circuit Flashcards

1
Q

If the line frequency of a parallel ac-
circuit is slightly less than the resonant
frequency, the circuit behaves as

A. capacitive
B. reactive
C. resistive
D. purely inductive

A

B. reactive

A parallel resonant circuit behaves
as follows:
@resonance or @f=fr → resistive
below resonance or @f<fr→inductive
above resonance or @f>fr→capacitive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Peak value divided by the rms value
gives us?

A. Peak factor
B. Neither peak nor crest factor
C. Both peak and crest factor
D. Crest factor

A

C. Both peak and crest factor

Peak value divided by the rms value
gives us the peak or crest factor.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

For high frequencies of alternating
current, capacitor acts as?

A. Short circuit
B. Amplifier
C. Open circuit
D. Rectifier

A

A. Short circuit

Capacitive impedance is inversely
proportional to frequency. Hence at very
high frequencies, the impedance is
almost equal to zero, hence it acts as a
short circuit and there is no voltage
across it.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Parallel tuned circuits offer:

A. very high impedance at resonance
B. an impedance equal to resistance of the
circuit
C. low impedance at resonance
D. zero impedance at resonance

A

A. very high impedance at resonance

PARALLEL, TUNED. Question refers to Resonance. The one frequency at which Inductive Reactance cancels Capacitive Reactance. In a PARALLEL circuit, Impedance (Z) at resonance is HIGH (series circuit will be the opposite).
As a memory aid, try to visualize the PARALLEL circuit as a tub or tank, signals get trapped at resonance. Try to visualize the SERIES circuit as a slim tube, signals slip right through at resonance.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Apparent power in AC circuits should be
expressed in….

A. VAR
B. W
C. eV
D. VA

A

D. VA

VA - unit for Apparent Power
VAR - unit for Reactive/Imaginary Power
W - unit for Active/Real/True Power
ev - unit for Energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

A filter which attenuates all frequencies below a designated cut-off frequency fo and passes all other frequencies greater than fc is called?

A. band pass filter
B. low pass filter
C. high pass filter
D. band elimination filter

A

C. high pass filter

A filter is called high pass filter if
attenuates all frequencies below a designated cut-off frequency fc and passes all other frequencies greater than fc. Thus the pass band of this filter is the frequency range above fc and the stop band is the frequency range below fc.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Resonance is the condition that exists
when:

A. resistance is equal to the reactance
B. inductive reactance is the only opposition
in the circuit
C. the circuit contains no resistance
D. inductive reactance and capacitive
reactance are equal

A

D. inductive reactance and capacitive
reactance are equal

Resonance is the condition where
Inductive Reactance (XL) is equal in
value to Capacitive Reactance (XC). For a given Inductance (L, a coil or inductor) and Capacitance (C, a capacitor), resonance happens at one frequency: the resonant frequency. At resonance, the two reactances cancel each other only resistance is left in the circuit.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

When one sine wave passes through the
zero following the other, it is_____

A. Either leading or lagging
B. Lagging
C. Neither leading nor lagging
D. Leading

A

B. Lagging

The sine wave is said to lag because it passes though zero following the other,hence it crosses zero after the first wave, therefore it is said to lag.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

An RC coupling circuit is an example of
what type of filter?

A. Band pass filter
B. All pass filter
C. High pass filter
D. Low pass filter

A

C. High pass filter

An RC coupling circuit is an example of
a high-pass filter because the AC
component of the input voltage is
developed across R and the DC voltage
is blocked by the series capacitor.
Furthermore, with higher frequencies in the AC component, more AC voltage is coupled.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

In a series ac-circuit, if the line
frequency is more than the resonant
frequency, the circuit behaves as

A. capacitive
B. reactive
C. inductive
D. resistive

A

C. inductive

A series RLC circuit behaves
as follows:
@resonance or @f=fr →resistive
below resonance or @f<fr →capacitive
above resonance or @f>fr →inductive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

The circuit admittance Y = 0.2-j0.6, the
circuit is

A. resistive
B. reactive
C. inductive
D. capacitive

A

C. inductive

Since it is an admittance parameter, the
real part corresponds to conductance
and the imaginary part represents susceptance. The susceptance (imaginary part) is negative, therefore it is an inductive susceptance making the answer for this question inductive.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Current is maximum at_____ frequency of bandwidth

A. all end
B. middle
C. left end
D. right end

A

B. middle

Current will be maximum at a frequency which is at the middle of bandwidth. On both sides, it decreases and is 1/√2 times the maximum current at the ends of bandwidth.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

The current leads the supply voltage in a
series RLC circuit has its frequency _____ the resonant frequency.

A. Below
B. Equal to
C. Cannot be determined
D. Above

A

A. Below

Current is leading the voltage
indicates capacitor
dominating circuit.
XC>XL
Hence,
1/(wC)>wL
Therefore,
w<1/√LC
So, frequency less than
resonant frequency.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

When comparing rms voltages and
average voltages, which of the following
statement is true, assuming sine
waves?

A. The rms voltage is always greater than
the average voltage
B. Either the rms voltage or the average
voltage might be larger
C. The average voltage is always greater than
the rms voltage
D. There will always be a very large difference
between the rms voltage and the average
voltage

A

A. The rms voltage is always greater than
the average voltage

For sinusoidal waveforms, rms value =
0.707 of max or peak value

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

In filter circuits, the attenuation rate is
also called?

A. Roll in
B. Envelope delay
C. Ripple
D. Roll off

A

D. Roll off

Roll off is also called the attenuation
rate, roll-off is the rate of change of
amplitude with frequency in a filter.
The faster the roll-off, or the higher the
attenuation rate, the more selective the filter is, i.e., the better able it is to differentiate between two closely spaced signals, one desired and the other not.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

For a sharp resonance, bandwidth is_____

A. zero
B. high
C. infinity
D. low

A

D. low

For sharp resonance quality factor is
high and the quality factor is inversely
proportional to bandwidth so bandwidth
is low for sharp resonance.

17
Q

Active power in AC circuits should be
expressed in…

A. W
B. eV
C. VA
D. VAR

A

A. W

VA - unit for Apparent Power
VAR - unit for Reactive/Imaginary Power
W - unit for Active/Real/True Power
ev - unit for Energy

18
Q

A resistive and a capacitive load of
equal magnitude is connected in series,determine the phase difference between the voltage and the current.

A. current leads the voltage by 90°
B. current leads the voltage by 45°
C. current lags the voltage by 45°
D. current lags the voltage by 90°

A

B. current leads the voltage by 45°

Since X and R are equal, θ = arctan(X/R) = arctan (1/1) = 45 degrees. And since the circuit is capacitive, the current leads the voltage by this angle.
Therefore answer will be “current leads
the voltage by 45°

19
Q

In an RLC circuit, the power factor is
always_____

A. Depends on the cicruit
B. Negative
C. Zero
D. Positive

A

A. Depends on the cicruit

In an RLC series circuit, the power factor depends on the values of capacitances, resistances, and inductances in the
circuit. This depends also on how Rs, Ls, and Cs are connected. Hence in an RLC circuit, the power factor depends on the circuit.

20
Q

A filter that passes all frequencies lying
outside a certain range, while it
attenuates all frequencies between the
two designated frequencies is called?

A. low pass filter
B. band elimination filter
C. band pass filter
D. high pass filter

A

B. band elimination filter

A band elimination filter passes all
frequencies lying outside a certain
range, while it attenuates all frequencies
between the two designated
frequencies. It is also referred to as
band stop filter.

21
Q

In SI, quality factor is….

A. in Hz
B. unitless
C. in Farad
D. in in Siemen

A

B. unitless

Quality factor or Q factor is a
dimensionless parameter that describes
how underdamped an oscillator or
resonator is. It is defined as the ratio of the peak energy stored in the resonator in a cycle of oscillation to the energy
lost per radian of the cycle.

22
Q

Parallel tuned circuits offer:

A. an impedance equal to resistance of the
circuit
B. zero impedance at resonance
C. very high impedance at resonance
D. low impedance at resonance

A

C. very high impedance at resonance

In a parallel tuned circuit, current is
minimum because it offers maximum
impedance at resonance.
On the other hand, for a series resonant circuit, the current is maximum because it offers minimum impedance at resonance.

23
Q

What is the type of filter shown in the
figure? (AC circuits)

A. Low pass filter
B. High pass filter
C. Band pass filter
D. All pass filter

A

A. Low pass filter

A low-pass filter can also be implemented with an inductor and a resistor. At very low frequencies, the inductor has very low reactance compared to the resistance and therefore the attenuation is minimum.
Thus allowing lower frequencies to pass through while attenuating higher frequency
signals. The cutoff frequency is
determined by using the formula fco = R/2πL.

24
Q

For a sharp resonance, bandwidth is _____

A. zero
B. infinity
C. low
D. high

A

C. low

For sharp resonance quality factor is
high and the quality factor is inversely
proportional to bandwidth so bandwidth
is low for sharp resonance.

25
Q

When a series LCR circuit is tuned to the
frequency of the source, the:

A. line current leads the applied voltage
B. line current reaches maximum
C. impedance is maximum
D. line current lags the applied voltage

A

B. line current reaches maximum

SERIES, TUNED. Question refers to
Resonance. The one frequency at which Inductive Reactance cancels Capacitive Reactance. In a SERIES circuit, Impedance (Z) at resonance is LOW (parallel circuit will be the opposite). If Impedance is low (little total opposition), current will be high.
As a memory aid, try to visualize the SERIES circuit as a slim tube, signals slip right through at resonance. Try to visualize the PARALLEL circuit as a tub or tank signals get trapped at resonance.

26
Q

Which of the following statements is true if the frequency decreases in the circuit in a series RL circuit?

A. VR decreases.
B. IT decreases.
C. Vs decreases
D. The phase angle decreases.

A

D. The phase angle decreases.

As the frequency decreases in value,
inductive reactance of the inductor will
also decrease. A decrease in the
inductive reactance will result in a
decrease in the phase angle, since in a
series RL circuit phase angle is
calculated as tan(XL/R).

27
Q

Which of the following is true regarding
power factor?

A. it is equal to reactive factor for a purely
resistive condition
B. it is equal to the tangent of the phase
angle
C. it does not exist in AC circuits
D. it is a unitless quantity

A

D. it is a unitless quantity

Power factor is simple the cosine of the
angle of lead or angle of lag between
voltage and current. Therefore it is a
unitless quantity.

28
Q

At what angle does an alternating
voltage of cosine-waveform reaches its
negative peak?

A. 135°
B. 90°
C. 180°
D. 45°

A

C. 180°

From this figure, the cosine-
waveform reaches its
negative peak value at 0 = T or 180°.

see the figure on your gallery

29
Q

In an inductor, the reactive factor is _____

A. 0
B. 100
C. 1
D. Infinity

A

C. 1

In an inductor, the current is lagging by
90 degrees from the voltage.
The reactive factor is the sine of the angle between the voltage and the current. If the angle between the voltage and current is 90, then sin 90 = 1. Hence, the reactive factor is equal to 1.

30
Q

In the power triangle used in analyzing
AC circuits, the side of the triangle
opposite to phase angle is for…..

A. true power
B. reactive power
C. active power
D. apparent power

(go to your gallery for u to see the figure baby)

A

B. reactive power

31
Q

At resonance, bandwidth includes the
frequency range that allows _____
percent of the maximum voltage to flow.

A. 33.33
B. 50
C. 66.67
D. 70.7

A

D. 70.7

At resonance, bandwidth includes the
frequency range that allows 70.2
percent of the maximum voltage to flow.
This is because of the bandwidth
frequency range, the value of the
voltage is equal to the maximum value
of voltage divided by √2.

32
Q

As the impedance increases, the
admittance_____

A. Remains the same
B. Becomes zero
C. Increases
D. Decreases

A

D. Decreases

As the impedance increases, the
admittance decreases because
admittance is equal to 1/impedance.

33
Q

In a series RLC circuit, the phase
difference between the voltage across
the capacitor and the voltage across the
inductor is?

A. 0°
B 90°
C. 360°
D. 180°

A

D. 180°

In a series RLC circuit, voltage across
inductor lead the current by 90 and
voltage across capacitor lag the current by 900 so, the phase difference between the voltage across the inductor and the voltage across the capacitor is 180.

34
Q

In an RC series circuit_____

A. Applied voltage and capacitive voltage are
in phase
B. Applied voltage leads capacitor voltage
C. Current and voltage are in phase
D. Applied voltage lags capacitor voltage

A

B. Applied voltage leads capacitor voltage

In an RC circuit, the applied voltage
leads the current in the circuit, hence
the applied voltage leads the capacitive
voltage.

35
Q

In a sinusoidal wave, average current is
always _____ rms current.

A. Less than
B. Not related
C. Equal
D. Greater than

A

A. Less than

In sinusoidal waveforms, for one
alternation average value = 0.637Vm
and rms value = 0.707Vm. For one cyle,
average value = 0 and rms value =
0.707Vm. Therefore, we can say that “in
a sinusoidal wave, average current is
always LESS THAN rms current”.

36
Q

In an inductive circuit, the current_____
the voltage?

A. Leads
B. Is less than
C. Lags
D. Is greater than

A

C. Lags

In a pure inductive circuit the voltage
leads the current and the current lags
the voltage by a phase difference of 90
degrees.

37
Q

At resonance condition in a series tuned circuit, the voltage across the capacitor and inductor is ______ the source voltage

A. Much less than
B. Equal to
C Less than
D. Greater than

A

D. Greater than

In resonance condition, the voltage
across the capacitor and inductor is
greater than the source voltage because
the voltage across the capacitor or
inductor in resonance condition is equal
to Q times the source voltage.

38
Q

A coil and an air-spaced capacitor are
arranged to form a resonant circuit. The
resonant frequency will remain the
same if we:

A replace the air dielectric with oil in the
capacitor
B. add a resistor to the circuit
C. increase the area of plates in the capacitor
D. wind more turns on the coil

A

B. add a resistor to the circuit

Resonance is affected exclusively by Inductance (L in Henrys for inductors)and Capacitance (C in Farads for capacitors). “1” and “2” affect C. “3”
affects L. Only “4” has no impact on L nor C.

39
Q

In a sinusoidal wave, average value is
_____ dc value.

A. Greater than
B. Not related
C. Less than
D. Equal to

A

D. Equal to

Average value is also called DC value.
For one alternation of a sinusoidal
waveform this will be equal to 0.637 of the maximum or peak value but for one complete cycle this will be equal to zero.

ELEX (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions