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AC CIRCUITS EXCEL SOURCE Flashcards

PROBLEMS AND OBJECTIVE TYPE QUESTIONS

1
Q
  1. An incandescent lamp load generally
    considered to be made up of resistors
    take 4.8 kW from a 120 V AC
    source. What is the instantaneous
    maximum value of power?
    A. 4800 W C. 2400 W
    B. 480 W D. 9600W
A
  1. D. 9600 W
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2
Q

The p.f. of an RC circuit is ___.
A. often zero
B. between zero and 1
C. always unity
D. between zero and -1

A
  1. B. between zero and 1
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3
Q
  1. A 25-ohm resistor connected in series
    with a coil of 50 ohms resistance and
    150 mH inductance. What is the
    power factor of the circuit?
    A. 85% C. 80%
    B. 90% D. 75%
A
  1. C. 80%
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4
Q
  1. The length of time between a point in
    one cycle and the same point in the
    next cycle of an ac wave is the:
    A. Frequency C. Magnitude
    B. Period D. Polarity
A
  1. B. Period
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5
Q
  1. Which of the following can vary with
    ac, but not with dc?
    A. Power C. Voltage
    B. Frequency D. Magnitude
A
  1. B. Frequency
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6
Q
  1. Three loads, units A, B, and C are
    connected in parallel and take
    currents that are respectively 12, 10,
    and 15 A respectively. Assuming Ia
    to be the reference phasor. Ib leads by
    30o
    and Ic lags behind Ia by 65 degrees
    ,
    calculate the total (resultant) current.
    A. 28.33 A C. 30.21 A
    B. 26.46 A D. 32.10 A
A
  1. A. 28.33 A
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7
Q
  1. If R increases in an RC circuit, but
    the capacitance and the frequency are
    nonzero and constant, then the vector
    in the RC plane will:
    A. Get longer and rotate clockwise
    B. Get longer and rotate
    counterclockwise
    C. Get shorter and rotate clockwise
    D. Get shorter and rotate
    counterclockwise
A
  1. B. Get longer and rotate
    counterclockwise
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8
Q
  1. A 50 and 100-microfarad capacitors
    are connected in series and across a
    100 sin (ωt + 30o
    ) voltage. Write the
    equation of the current.
    A. 1.26 sin (ωt + 120o)
    B. 1.26 sin (ωt + 90o)
    C. 5.65 sin (ωt + 120o)
    D. 5.56 sin (ωt + 90o)
A
  1. A. 1.26 sin (ωt + 120o
    )
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9
Q
  1. On a spectrum analyzer, a pure ac
    signal, having just one frequency
    component, would look like:
    A. A single pip
    B. A perfect sine wave
    C. A square wave
    D. A sawtooth wave
A
  1. A. A single pip
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10
Q

10.If admittance Y = 0.06 – j0.08 mho,
then conductance G equals,
A. – 0.06 C. 0.06
B. 0.08 D. – 0.08

A
  1. C. 0.06
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11
Q
  1. Three-phase ac:
    A. Has waves that add up to three
    times the originals
    B. Has three waves, all of the same
    magnitude
    C. Is what you get at a common wall
    outlet
    D. Is of interest only to physicists
A
  1. B. Has three waves, all of the same
    magnitude
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12
Q
  1. A parallel circuit consists of a
    resistor having a conductance of 4
    mhos, an inductive reactor having a
    susceptance of 8 mhos and a
    capacitive reactor having a
    susceptance of 5 mhos. What is the
    impedance of the circuit?
    A. 0.11 + j0.13
    B. 0.13 + j0.11
    C. 0.12 + j0.16
    D. 0.16 + j0.12
A
  1. D. 0.16 + j0.12
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13
Q
  1. The period of an ac wave is:
    A. The same as the frequency
    B. Not related to the frequency
    C. Equal to 1 divided by the
    frequency
    D. Equal to the amplitude divided by
    the frequency
A
  1. C. Equal to 1 divided by the
    frequency
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14
Q
  1. An industrial coil has a resistance of
    32 ohms and a reactance of 24 ohms
    and rated 440 volts at 60 Hz. A
    factory will connect the coil to a 440
    V, 50 Hz supply. Solve for the value
    of a series resistor needed to avoid
    overcurrent condition.
    A. 2.07 Ω C. 2.64 Ω
    B. 2.44 Ω D. 2.25 Ω
A
  1. C. 2.64 Ω
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15
Q
  1. A triangular wave:
    A. Has a fast rise time and a slow
    decay time
    B. Has a slow rise time and a fast
    decay time
    C. Has equal rise and decay rates
    D. Rises and falls abruptly
A
  1. C. Has equal rise and decay rates
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16
Q
  1. A non-inductive resistor R is
    connected in parallel with an
    inductive reactance of 10 ohms. The
    combination is then connected in
    series with a capacitive reactance of
    5 ohms. The whole combination is
    connected across a 100-V, 60 Hz AC
    source. If R is equal to 5 ohms, solve
    for the voltage across the parallel
    combination.
    A. 87.53 V C. 88.34 V
    B. 89.44 V D. 91.87 V
A
  1. B. 89.44 V
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17
Q

17.If two waves have the same
frequency and the same amplitude,
but opposite phase, the composite
wave is:
A. Twice the amplitude of either
wave alone
B. Half the amplitude of either wave
alone
C. A complex waveform, but with
the same frequency as the
originals
D. Zero

A
  1. D. Zero
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18
Q

18.If R increases in an RC circuit, but
the capacitance and the frequency are nonzero and constant, then the vector
in the RC plane will:
A. Get longer and rotate clockwise
B. Get longer and rotate
counterclockwise
C. Get shorter and rotate clockwise
D. Get shorter and rotate
counterclockwise

A
  1. B. Get longer and rotate
    counterclockwise
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19
Q
  1. An advantage of ac over dc in utility
    applications is:
    A. Ac is easier to transform from one
    voltage to another
    B. Ac is transmitted with lower loss
    in wires
    C. Ac can be easily gotten from dc
    generators
    D. Ac can be generated with less
    dangerous by-products
A
  1. A. Ac is easier to transform from
    one voltage to another
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20
Q
  1. A 240 V, 25 Hz sinusoidal generator
    is connected to a 20 ohms resistor.
    Determine the instantaneous current
    when elapsed time is 0.01 second.
    A. 15.43 A C. 16.30 A
    B. 16.97 A D. 12.00 A
A
  1. B. 16.97 A
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21
Q
  1. As the frequency of a wave gets
    lower, all other things being equal,
    the value of XC for a capacitor:
    A. Increases negatively
    B. Decreases negatively
    C. Does not change
    D. Depends on the current
A
  1. A. Increases negatively
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22
Q
  1. Each impedance R + jXL:
    A. Corresponds to a unique point in
    the RL plane
    B. Corresponds to a unique
    inductance reactance
    C. Corresponds to a unique
    resistance
    D. All of the above
A
  1. D. All of the above
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23
Q
  1. An impedance draws a current i = 10
    cos (ωt – 30o) from a voltage v = sin
    ωt. What is the maximum power?
    A. 2200 W C. 1100 W
    B. 190.5 W D. 1320 W
A
  1. C. 1100 W
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24
Q
  1. A resistor of 6 ohms and an unknown
    impedance coil in series draws 12 A
    from a 120-V, 60-Hz line. If the real
    power taken from the line is 1152
    watts, what is the coil inductance?
    A. 15.9 mH C. 10.0 mH
    B. 20.0 mH D. 1.59 mH
A
  1. A. 15.9 mH
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25
Q
  1. Two waves are in phase coincidence.
    One has a peak value of 3V and the
    other a peak value of 5V. The
    resultant will be:
    A. 8 V peak, in phase with the
    composites
    B. 2 V peak, in phase with the
    composites
    C. 8 V peak, in phase opposition
    with respect to the composites
    D. 2 V peak, in phase opposition
    with respect to the composites
A
  1. A. 8 V peak, in phase with the
    composites
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26
Q

26.In vector diagrams, the progression
of time is sometimes depicted as:
A. Movement to the right
B. Movement to the left
C. Rotation counterclockwise
D. Rotation clockwise

A
  1. C. Rotation counterclockwise
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27
Q
  1. A capacitance is connected to a 115
    V, 25 Hz mains and takes 5 A. What
    current will it take when the
    capacitance and the frequency are
    both doubled?
    A. 2.5 A C. 5 A
    B. 20 A D. 10 A
A
  1. B. 20 A
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28
Q
  1. A resistance of 5 ohms is connected
    in series with a capacitor of 442.1 μF.
    The combination is then connected in
    parallel with an inductance of 21.22
    mH. Solve for the resultant current if
    the circuit is connected across a 120
    V, 60 Hz AC source.
    A. 9.44 A C. 10.68 A
    B. 11.29 A D. 10.34 A
A
  1. D. 10.34 A
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29
Q
  1. Given three impedances: Z1 = 10 +
    j0, Z2 = 3 + j4 and Z3 = 8 – j6.
    Impedance Z2 and Z3 are connected
    in parallel and that combination is
    connected in series with impedance
    Z1 across 120 V single-phase 60 Hz
    source. Find the total power drawn
    by the impedances.
    A. 1008 W C. 1204 W
    B. 1038 W D. 1103 W
A
  1. A. 1008 W
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30
Q

30.In a purely reactive circuit, the phase
angle is ___.
A. increasing C. decreasing
B. 0 degrees D. 90

A
  1. D. 90
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31
Q

31.If e = 100 sin (wt + 30o) – 50 cos 3wt+ 25 sin (5wt + 150o) and i = 20 sin
(wt + 40o) + 10 sin (3wt + 30o) – 5
sin (5wt – 50o). Calculate the power
in watts.
A. 1177 C. 918.5
B. 1043 D. 922.4

A
  1. C. 918.5
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32
Q

32.In a purely resistive circuit, the phase
angle is ____.
A. increasing C. decreasing
B. 0 degrees D. – 90

A
  1. B. 0 degrees
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33
Q

33.In vector diagrams, the progression
of time is sometimes depicted as:
A. Movement to the right
B. Movement to the left
C. Rotation counterclockwise
D. Rotation clockwise

A
  1. C. Rotation counterclockwise
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34
Q
  1. A series circuit composed of a 0.2
    henry inductor and a 74-microfarad
    capacitor is connected to a 60 V
    variable frequency source. At what
    frequency is the current be 4 amperes
    with a lagging power factor?
    A. 50 Hz C. 51 Hz
    B. 48 Hz D. 49 Hz
A
  1. B. 48 Hz
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35
Q

35.In vector diagrams, the progression
of time is sometimes depicted as:
A. Movement to the right
B. Movement to the left
C. Rotation counterclockwise
D. Rotation clockwise

A
  1. C. Rotation counterclockwise
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36
Q
  1. What is the wavelength of the carrier
    frequency of 100 MHz?
    A. 3.0 m C. 7.5 m
    B. 1.5 m D. 6.0 m
A
  1. A. 3.0 m
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37
Q
  1. The impedance vector 0 – j22
    represents:
    A. A pure resistance
    B. A pure inductance
    C. A pure capacitance
    D. An inductance combined with a
    resistance
A
  1. C. A pure capacitance
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38
Q
  1. Across a 230 V, 60 Hz powers
    supply is a 15-ohm non-inductive
    resistor. What is the equation of the
    resulting current?
    A. 21.68 sin 377t
    B. 26.55 sin 377t
    C. 15.33 sin 377t
    D. 28.16 sin 377t
A
  1. A. 21.68 sin 377t
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39
Q
  1. Each point in the RL plane:
    A. Corresponds to a unique
    resistance
    B. Corresponds to a unique
    inductance
    C. Corresponds to a unique
    combination of resistance and
    inductive reactance
    D. Corresponds to a unique
    combination of resistance and
    inductance
A
  1. C. Corresponds to a unique
    combination of resistance and
    inductive reactance
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40
Q
  1. Three impedances Za = 3+ j4 ohms,
    Zc = 4 – j4 ohms and Zr = 0 + j3
    ohms are connected in parallel. Solve
    for the PF of the combination.
    A. 0.653 leading
    B. 0.554 lagging
    C. 0.503 leading
    D. 0. 620 lagging
A
  1. B. 0.554 lagging
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41
Q

41.In vector diagrams, length of the
vector represents:
A. Average amplitude
B. Frequency
C. Phase difference
D. Peak amplitude

A
  1. D. Peak amplitude
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42
Q
  1. A capacitor is rated 100 kVAR, 380
    volts, 50 Hz. What will its rating be
    at 60 Hz, 220 volts?
    A. 50 kVAR
    B. 40 kVAR
    C. 90.9 kVAR
    D. 57.7 kVAR
A
  1. B. 40 kVAR
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43
Q
  1. A sine wave:
    A. Always has the same general
    appearance
    B. Has inductance
    C. Is in the same phase as a cosine
    wave
    D. Rises very fast, but decays slowly
A
  1. A. Always has the same general
    appearance
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44
Q

44.If the resistance R and the inductance
reactance XL both vary from zero to
unlimited values, but are always in
the ratio 3:1, the points in the RL
plane for all the resulting impedances
will fall along:
A. A vector pointing straight up
B. A vector pointing “east”
C. A circle
D. A ray of unlimited length

A
  1. D. A ray of unlimited length
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45
Q

45.If two waves have the same
frequency and the same phase, the
composite wave:
A. Has a magnitude equal to the
difference between the two
originals
B. Has a magnitude equal to the sum
of the two originals
C. Is complex, with the same
frequency as the originals
D. Is zero

A
  1. B. of the two originals
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46
Q
  1. Which of the following is not a
    general characteristic of an ac wave?
    A. The wave shape is identical for
    each cycle
    B. The polarity reverses periodically
    C. The electrons always flow in the
    same direction
    D. There is a definite frequency
A
  1. C. The electrons always flow in the
    same direction
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47
Q
  1. A resistor and a capacitor are
    connected in series across a supply of
    250 V. When the supply frequency is
    50 Hz the current in the circuit is 5
    A. When the supply frequency is 60
    Hz, the current is 5.8 A. Find the
    value of the capacitance.
    A. 58.3 μF C. 60.2 μF
    B. 69.1 μF D. 70.2 μF
A
  1. B. 69.1 μF
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48
Q

48.In a perfect sine wave, the pk-pk
value is:
A. Half of the peak value
B. The same as the peak value
C. 1.414 times the peak value
D. Twice the peak value

A
  1. D. Twice the peak value
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49
Q
  1. A circuit consists of Xa = j5 ohms, Xc
    = - 5j ohms and R = 5 ohms all are
    connected in parallel. Find the
    equivalent impedance.
    A. 5.5 Ω C. 5.0 Ω
    B. 4.8 Ω D. 5.2 Ω
A
  1. D. Twice the peak value
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50
Q
  1. A 1-hp, 220 V, 60 Hz capacitor-start
    motor has main and auxiliary
    winding impedance at starting of 3.5
    + j2.5 ohms and 8.6 + j2.5 ohms,
    respectively. Determine the value of
    the starting capacitance that will
    place the main and auxiliary winding
    currents 90o
    apart at starting.
    A. 186.75 μF
    B. 174.35 μF
    C. 182.43 μF
    D. 170.67 μF
A
  1. C. 182.43 μF
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51
Q
  1. The rms value of sine wave is equal
    to _____.
    A. 0.637 max value
    B. 0.606 max value
    C. 0.707 max value
    D. 1.414 max value
A
  1. C.0.707 max value
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52
Q
  1. The instantaneous equation of a
    voltage is given as 325.3 sin(377t)
    volts. What is the rms value of the
    voltage?
    A. 325.3 volts
    B. 460 volts
    C. 212 volts
    D. 230 volts
A
  1. D. 230 volts
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53
Q
  1. The instantaneous value of a voltage
    is given as 100sin377t volts. What is
    its average value?
    A. 63.7 volts
    B. 70.7 volts
    C. 50 volts
    D. 122 volts
A
  1. A. 63.7 volts
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54
Q
  1. The average value of a sinusoidal
    current is 100 amperes. What is its
    rms value?
    A. 64 A
    B. 141.4 A
    C. 88.8 A
    D. 111 A
A
  1. D. 111 A
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55
Q
  1. What is the complex expression for a
    given alternating current, i =
    250sin(ωt+25°)?
    A. 227+j106 A
    B. 160 – j75 A
    C. 227 – j106A
    D. 160+j75 A
A
  1. D. 160+j75 A
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56
Q
  1. The voltage in a circuit follows the
    law v = 200sinωt. If the frequency is
    50Hz, how long will it take for the
    voltage to rise to 120 volts?
    A. 0.002 s
    B. 0.02 s
    C. 0.2 s
    D. 2 s
A
  1. A. 0.002 s
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57
Q
  1. The rms value of a sinusoidal AC
    current is equal to its value at an
    angle of _____ degrees.
    A. 30
    B. 45
    C. 60
    D. 90
A
  1. B. 45
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58
Q
  1. The rms value and mean value is the
    same in the case of _____.
    A. Triangular wave
    B. Cosine wave
    C. Square wave
    D. Half wave rectified sine wave
A
  1. C. Square wave
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59
Q
  1. An ac voltage of 60Hz has a
    maximum value of 100V. Its value
    after 1/300 second after the instant
    the current is zero will be _____.
    A. 25 V
    B. 50 V
    C. 95.1 V
    D. 77.9 V
A
  1. C. 95.1 V
60
Q
  1. An alternating voltage is given by v
    = 30 sin314t. What is the time taken
    by the voltage to reach 30 volts for
    the first time?
    A. 0.005 s
    B. 0.02 s
    C. 0.03 s
    D. 0.1 s
A
  1. A. 0.005 s
61
Q
  1. What is the form factor of half wave
    rectified sinusoidal wave?
    A. 1.57
    B. 1.11
    C. 1.0
    D. 1.15
A
  1. A. 1.57
62
Q
  1. A circuit carries a direct current of 10
    amperes on which is super imposed
    in a sinusoidal component of 5
    ampere maximum value. What is the
    value of the rms effective current?
    A. 8.2 A
    B. 10.6 A
    C. 12.74 A
    D. 14.14 A
A
  1. B. 10.6 A
63
Q
  1. A purely resistive circuit has an
    impedance of ____
    A. Z=R+jXL
    B. Z= R-jXC
    C. Z=R
    D. Z=R+j(XL-XC)
A
  1. C. Z=R
64
Q
  1. In a purely inductive circuit _____.
    A. the current leads the voltage by
    90 degrees.
    B. the is in phase with the voltage
    C. the current can either lag or lead
    the voltage by 90 degrees.
    D. the current lags the voltage by 90
    degrees.
A
  1. D. the current lags the voltage by
    90 degrees.
65
Q
  1. Which of the following circuit
    component opposes the change in the
    circuit voltage?
    A. Resistance
    B. Inductance
    C. Capacitance
    D. Impedance
A
  1. C. Capacitance
66
Q
  1. Actual power is zero in _____.
    A. a purely inductive circuit
    B. a purely resistive circuit
    C. an impedance that has a
    resistance of 10 ohms and
    capacitance of 10 microfarads
    D. an impedance that has a
    resistance of 10 ohms and
    inductance of 10 millihenry.
A
  1. A. a purely inductive circuit
67
Q
  1. A 240-volt, 60Hz, source, is
    supplying an impedance of 3.5+j2
    ohms. What will be the value of the
    current when the resistance is
    reduced to by 50%?
    A. 55 A
    B. 90 A
    C. 72.4 A
    D. 66.7 A
A
  1. B. 90 A
68
Q
  1. What is the reactance of a 50mH
    inductance connected to a 100-volt
    source, 50Hz?
    A. 12.8 ohms
    B. 18.85 ohms
    C. 37.7 ohms
    D. 15.7 ohms
A
  1. D. 15.7 ohms
69
Q
  1. A 60mH inductance is connected in
    series with a 10-ohm resistor. If the
    voltage is 220 volts, 60Hz, what is
    the current drawn?
    A. 6 A
    B. 8 A
    C. 10 A
    D. 12 A
A
  1. B. 8 A
70
Q
  1. Determine the power angle in the
    series circuit which consist of R=25
    ohms and L=0.2H across a power
    supply of 220V, 60Hz.
    A. 71.7 degrees
    B. 46.6 degrees
    C. 32.3 degrees
    D. 56.2 degrees
A
  1. A. 71.7 degrees
71
Q
  1. What is the reactance of an ac circuit
    having 20 ohms inductive reactance
    and 10 ohms capacitive reactance?
    A. 5 ohms
    B. 10 ohms
    C. 20 ohms
    D. 30 ohms
A
  1. B. 10 ohms
72
Q

22.Find the value of impedance which
requires -1540 VAR at 230V and
10A.
A. 17.4 – j15 ohms
B. 16.8 – j15.7 ohms
C. 17.52 – j 14.5 ohms
D. 17.09 – j 15.4 ohms

A
  1. D. 17.09 – j 15.4 ohms
73
Q
  1. A single-phase circuit is supplied
    from a 220V, 60Hz, source. It draws
    2000 watts of power and 10 amperes
    of current. What is the power factor
    of the circuit?
    A. 90.9%
    B. 72.5%
    C. 82.8%
    D. 41.14%
A
  1. A. 90.9%
74
Q
  1. The input of an AC circuit having
    power factor of 0.8 lagging is
    40kVA. The power drawn by the
    circuit is _____.
    A. 12 kW
    B. 20 kW
    C. 32 kW
    D. 36 kW
A
  1. C. 32 kW
75
Q
  1. The apparent power drawn by an AC
    circuit is 10kVA and active power is
    8kW. The reactive power in the
    circuit is _____.
    A. 4 kVAR
    B. 8 kVAR
    C. 6 kVAR
    D. 12 kVAR
A
  1. C. 6 kVAR
76
Q
  1. A coil is connected across a
    200V,50Hz supply and takes a
    current of 10A. The loss in the coil is
    1000W. The impedance and
    resistance of the coil are _____.
    A. 10 & 8
    B. 15 & 8
    C. 10 & 10
    D. 20 & 10
A
  1. D. 20 & 10
77
Q
  1. An electric iron designed for 110V
    AC supply was rated at 500 Watts. It
    was then connected across 220V
    supply. Assuming an ideal scenario,
    what will be the new wattage?
    A. 2000 Watts
    B. 2500 Watts
    C. 500 Watts
    D. 250 Watts
A
  1. A. 2000 Watts
78
Q
  1. A 40-micro-farad capacitor, 100-
    millihenry inductance and a 20-ohm
    resistance are connected in series. At
    220-volt,60Hz, what is the current of
    the circuit?
    A. 6.3 Amperes
    B. 4.47 Amperes
    C. 5.78 Amperes
    D. 7.2 Amperes
A
  1. A. 6.3 Amperes
79
Q
  1. A coil connected in series with a
    resistance are supplied from a 240-
    volt, 60Hz source. The voltage across
    the resistance and the coil are both
    equal to 160 volts. If the circuit
    draws 1 Ampere from the source, what will be the value of coil
    resistance?
    A. 20
    B. 60
    C. 30
    D. 45
A
  1. A. 20
80
Q

30.For a series RLC circuit with
elements R=50Ω, L=8mH,
C=2.22μF. What is the equivalent
impedance of this circuit at 796Hz?
A. 50 + j50 ohms
B. 50+j120 ohms
C. 50 – j50 ohms
D. 50 – j120 ohms

A
  1. C. 50 – j50 ohms
81
Q
  1. In a series resonant circuit, the
    impedance of the circuit is _____.
    A. maximum
    B. minimum
    C. zero
    D. approaching infinity
A
  1. B. minimum
82
Q
  1. In a series circuit on resonance, the
    following will occur except _____.
    A. V=VR
    B. XL=XC
    C. VL=VR
    D. Z=R
A
  1. C. VL=VR
83
Q
  1. At resonance, a series RLC circuit
    has
    A. ω
    2LC=1
    B. ωLC=1
    C. ωL2C=1
    D. ω
    2L
    2C=1
A
  1. A. ω2LC=1
84
Q
  1. An 8Ω resistance, 16Ω inductive
    reactance and an unknown capacitor
    are connected in series across a
    100V, 50Hz supply. The current
    drawn by the circuit is 12.5 A. The
    value of capacitance of the capacitor
    at resonance is
    A. 50 μF
    B. 150 μF
    C. 200 μF
    D. 250 μF
A
  1. C. 200 μF
85
Q
  1. Impedance ZC is connected in series
    to the two impedances ZA=10+j10Ω
    and ZB=20 – j30Ω that are connected
    in parallel. What should be the value
    of impedance ZC to produce
    resonance?
    A. – j13.1
    B. j13.1
    C. j5.4
    D. – j5.4
A
  1. D. – j5.4
86
Q
  1. A 100-pF capacitor is connected in
    series with a coil having inductance
    of 100 μH and a resistance of 100Ω. At what frequency will this network
    have a unity pf?
    A. 1.3 MHz
    B. 1.5 MHz
    C. 1.23 MHz
    D. 1.6 MHz
A
  1. D. 1.6 MHz
87
Q
  1. The resistance of 50 ohms,
    inductance of 50 mH and capacitance
    of 50 micro-farads are connected in
    series across a 240-volt source. What
    is the resonant frequency?
    A. 100 Hz
    B. 50 Hz
    C. 1000 Hz
    D. 37.7 Hz
A
  1. A. 100 Hz
88
Q
  1. Two impedances Z1=2+j4 and
    Z2=R+j0 are connected in parallel.
    Determine R so that the pf of the
    circuit is 0.9 lagging.
    A. 2.4 ohms
    B. 3.2 ohms
    C. 4.2 ohms
    D. 6.5 ohms
A
  1. B. 3.2 ohms
89
Q
  1. A source of 200 volts rms is
    supplying a resistance of 50 ohms in
    parallel with a 150 mH inductor. To
    what angle is the current lag or lead?
    A. 41.48 leading
    B. 46.7 lagging
    C. 46.7 leading
    D. 41.48 lagging
A
  1. D. 41.48 lagging
90
Q
  1. Three loads are connected in parallel
    across 1400V rms, 60Hz, single
    phase supply.
    Load 1: Inductive load, 125kVA at
    0.28 pf
    Load 2: Capacitive load, 10kW and
    40kVAR
    Load 3: Resistive load, 15kW
    What is the total power factor?
    A. 60% lagging
    B. 60% leading
    C. 48% lagging
    D. 75% leading
A
  1. A. 60% lagging
91
Q
  1. A single-phase induction motor is
    rated 5Hp, 75% power factor and 220
    volts. What approximate size of
    capacitor is necessary to raise the
    power factor to about 95%?
    A. 2 kVAR
    B. 2.5 kVAR
    C. 3 kVAR
    D. 3.5 kVAR
A
  1. A. 2 kVAR
92
Q
  1. A load of 10,000 kVA, 85% power
    factor lagging is connected to a
    13,200-volt, line. How much reactive
    power is needed to correct the power
    factor to 97% lagging?
    A. 5,160 kVAR
    B. 2, 600 kVAR
    C. 3,140 kVAR
    D. 4,750 kVAR
A
  1. C. 3,140 kVAR
93
Q
  1. A 5Hp, 220V, 60Hz, single-phase
    induction motor, operates at an
    efficiency and power factor or 0.88
    and 0.8 respectively. What
    capacitance should be connected
    across the motor in order for the
    feeder supplying this motor to
    operate at unity power factor?
    A. 321.55 μF
    B. 163.62 μF
    C. 174.22 μF
    D. 112.86 μF
A
  1. C. 174.22 μF
94
Q
  1. A plant has a load of 290 kW with an
    average power factor of 70%. The
    owner requests you to correct the
    power factor to reduce its power
    consumption. How much reactive
    power in kVAR is required to
    increase the power factor to 90%?
    A. 155.39
    B. 162.75
    C. 150.34
    D. 154.58
A
  1. A. 155.39
95
Q

45.Poor power factor results to the
following except _____.
A. Reduces load handling capacity
of electrical system.
B. Overloads alternators,
transformers and distribution
lines.
C. Results to additional power
losses in the line.
D. Results into lesser voltage drop
across the lines.

A
  1. D. Results into lesser voltage drop
    across the lines.
96
Q

The length of time between a point in one cycle and the same point in the next cycle of an ac wave is the:
A. Frequency
B. Magnitude
C. Period
D. Phase

A

Period

97
Q

What is the term used to identify an AC voltage that would cause the same heating in a resistor as a corresponding value of DC voltage?
A. Root mean sqaure
B. Average Value
C. Maximum Value
D. Size

A

Root mean square (RMS)

98
Q

Two relays each with 20 ohms resistance and 0.16 H inductance are connected in series. What is the equivalent impedance?

A

40 + j120.63

99
Q

The ohmic resistance of a large magnetic contactor is measured to be 20 Ω. A 230 V is impressed on the contractor and the current is taken as 3.2 A. Neglecting core loss, determine the inductance of the contactor.
AC 1 - EXAMS

A

183 mH

100
Q

5 What is the wavelength of a carrier wave with a frequency of 100 MHz?

A

3 m

101
Q

6 Across a 230 V, 60 Hz power supply is a 15 Ω non-inductive resistor. What is the equation of the voltage and the resulting current?

A

e = 325.5 sin 377t, i = 21.6 sin 377t

102
Q

7 A sinusoidal current wave has a maximum value of 12.7 A. What is the average value of one-half cycle?

A

8.085

103
Q

8 A voltage wave is given by v(t) = 100 sin 314t. How long does it take this waveform to complete one-fourth cycle?

A

5 ms

104
Q

9 A resistor and a coil are connected in series with a voltage source. If the voltage across the coil is 10 sin (866t + 70°) V and the current flowing thru the resistor is 2 cos (866t - 80°) A, what is the resistance of the coil?

A

5 Ω

105
Q

10 What part of an alternating current is defined as a current which will produce the same heating effect as an equivalent direct current?

A

Effective value

106
Q

11 The period of an ac wave is:

A

Equal to 1 divided by the frequency

107
Q

12 If two waves have the same frequency and the same phase, the composite wave:

A

Has a magnitude equal to the sum of the two originals

108
Q

13 A rotating vector is known as a/an ______.

A

phasor

109
Q

14 What is the complex expression for a given alternating current, i = 15 sin (ωt – 15°)?

A

14.49 – j3.88

110
Q

15 The average value of a symmetrical alternating quantity, (such as a sine wave), is the average value measured over a ____ cycle.

A

half

111
Q

16 Calculate the effective value of v(t) = 100 sin 400t + 50 sin 800t + 10 cos 1200t V.

A

79.4V

112
Q

17 Which of the following can vary with ac, but not with dc?

A

Frequency

113
Q

18 If two waves have the same frequency and the same amplitude, but opposite phase, the composite wave is:

A

Zero

114
Q

19 A telephone circuit makes power available at a pair of terminals. The open circuit voltage across the terminals in 1 V and the impedance looking into the terminals is 500 – j500 Ω. What is the maximum power than can be drawn from the circuit?

A

0.001 W

115
Q

20 What figure of merit describes the ratio of the maximum value and the rms value?

A

Peak factoR

116
Q

21 A 240-V, 25 Hz sinusoidal generator is connected to a 20 Ω resistor. Determine the instantaneous current when elapsed time is 0.01 s.

A

16.97 A

117
Q

22 On a spectrum analyzer, a pure ac signal, having just one frequency component, would look like:

A

A single pip

118
Q

24 An advantage of ac over dc in utility applications is:

A

AC is easier to transform from one voltage to another

119
Q

25 Two current sources deliver current to a common load. The first source delivers a current whose equation is 25 sin 100πt A while the second delivers a current whose equation is 15 cos 100πt A. What is the rms value of the current in the load?

A

20.6 A

120
Q

1 The ohmic resistance of a coil is measured to be 5 Ω. A 115 V is impressed on the coil and the current is taken as 7.6 A. Determine the inductance of the circuit.

A

37.9 mH

121
Q

2 As the number of turns in a coil increases, the current in the coil will eventually _____.

A

decrease to near zero

122
Q

Each impedance R – jXc:

A

Represents a unique combination of resistance and reactance

123
Q

What is the complex expression for a given voltage equation, v = 311 cos (ωt – 15°)?

A

56.917 + j212.417

124
Q

5 What is the average value of a half-wave rectified sinusoidal curve with maximum value of 20 V?

A

6.366 V

125
Q

6 If R increases in an RC circuit, but Xc is always zero, then the vector in the RC plane will:

A

Always point straight towards the right

126
Q

7 A wire carries a current, i = 3 cos 314t A. What is the average current over 6 s?

A

0

127
Q

8 Find the average voltage in a resistance R = 10 ohms if the current in series form is i = 10 sin ωt + 5 sin 3ωt + 2 sin 5ωt A.

A

80.311 V

128
Q

9 As the number of turns in a coil increases, the reactance ______.

A

increases

129
Q

10 A resistor and an inductor are connected in series with a voltage source. If the voltage across the coil is 10 sin 377t V and the current flowing thru the resistor is 2 cos (377t - 80°) A, what is the resistance?

A

4.7 Ω

130
Q

11 Each point in the RC plane:

A

Corresponds to a unique combination of resistance and reactance

131
Q

12 A series RL circuit has L = 2 mH and an impedance of 15 Ω. When a sinusoidal voltage is applied, the current lags the voltage by 45°. What is the value of the angular frequency?

A

5300 rad/s

132
Q

13 If the dielectric material between the plates of a capacitor is changed, all other things being equal:

A

You can`t say what happens to Xc without more data

133
Q

14 As the size of the plates in a capacitor increase, all other things being equal:

A

The value of Xc decreases negatively

134
Q

15 Determine the effective value of v(t) = 150 + 100 sin ωt.

A

165.83 V

135
Q

16 The effective voltage across a circuit element is 100 + j50 V and the effective current through the element is 4 + j3 A. Calculate the reactive power taken by the element.

A

100 VAR leading

136
Q

17 As the frequency of a wave gets lower, all other things being equal, the value of Xc for a capacitor ______.

A

increases negatively

137
Q

18 In an RC circuit, as the ratio of capacitive reactance to resistance, - Xc/R, gets closer to zero, the phase angle ________.

A

gets closer to 0 degrees

138
Q

19 As the frequency of an ac wave gets lower, the value of X_L for a particular coil _____.

A

decreases

139
Q

20 Each point in the RL plane:

A

Corresponds to a unique combination of resistance and inductive reactance

140
Q

21 A circuit makes power available at a pair of terminals. The open circuit voltage across the terminals in 5 V and the impedance looking into the terminals is 500 – j500 Ω. What is the apparent power than can be drawn from the circuit?

A

0.035 VA

141
Q

22 Which of the following effects are generally less for an alternating current than for a direct current?

A

Chemical effects

142
Q

23 If R increases in an RC circuit, but the capacitance and the frequency are nonzero and constant, then the vector in the RC plane will:

A

Get longer and rotate counterclockwise

143
Q

24 A series RL circuit has L = 0.02 H and an impedance of 17.85 Ω. When a sinusoidal voltage is applied, the current lags the voltage by 63.5°. What is the value of the angular frequency?

A

800 rad/s

144
Q

25 An impedance draws a current i = 10 cos (ωt – 45°) A from a v = 220 sin ωt V. What is the apparent power?

A

1100 VA

145
Q
A

EE EXCEL SOURCE (5 decks)

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