AC CIRCUITS EXCEL SOURCE Flashcards
PROBLEMS AND OBJECTIVE TYPE QUESTIONS
- 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
- D. 9600 W
The p.f. of an RC circuit is ___.
A. often zero
B. between zero and 1
C. always unity
D. between zero and -1
- B. between zero and 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%
- C. 80%
- 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
- B. Period
- Which of the following can vary with
ac, but not with dc?
A. Power C. Voltage
B. Frequency D. Magnitude
- B. Frequency
- 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. 28.33 A
- 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
- B. Get longer and rotate
counterclockwise
- 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. 1.26 sin (ωt + 120o
)
- 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. A single pip
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
- C. 0.06
- 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
- B. Has three waves, all of the same
magnitude
- 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
- D. 0.16 + j0.12
- 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
- C. Equal to 1 divided by the
frequency
- 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
- C. 2.64 Ω
- 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
- C. Has equal rise and decay rates
- 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
- B. 89.44 V
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
- D. Zero
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
- B. Get longer and rotate
counterclockwise
- 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. Ac is easier to transform from
one voltage to another
- 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
- B. 16.97 A
- 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. Increases negatively
- 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
- D. All of the above
- 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
- C. 1100 W
- 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. 15.9 mH
- 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. 8 V peak, in phase with the
composites
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
- C. Rotation counterclockwise
- 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
- B. 20 A
- 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
- D. 10.34 A
- 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. 1008 W
30.In a purely reactive circuit, the phase
angle is ___.
A. increasing C. decreasing
B. 0 degrees D. 90
- D. 90
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
- C. 918.5
32.In a purely resistive circuit, the phase
angle is ____.
A. increasing C. decreasing
B. 0 degrees D. – 90
- B. 0 degrees
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
- C. Rotation counterclockwise
- 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
- B. 48 Hz
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
- C. Rotation counterclockwise
- 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. 3.0 m
- 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
- C. A pure capacitance
- 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. 21.68 sin 377t
- 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
- C. Corresponds to a unique
combination of resistance and
inductive reactance
- 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
- B. 0.554 lagging
41.In vector diagrams, length of the
vector represents:
A. Average amplitude
B. Frequency
C. Phase difference
D. Peak amplitude
- D. Peak amplitude
- 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
- B. 40 kVAR
- 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. Always has the same general
appearance
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
- D. A ray of unlimited length
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
- B. of the two originals
- 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
- C. The electrons always flow in the
same direction
- 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
- B. 69.1 μF
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
- D. Twice the peak value
- 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
- D. Twice the peak value
- 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
- C. 182.43 μF
- 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
- C.0.707 max value
- 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
- D. 230 volts
- 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. 63.7 volts
- 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
- D. 111 A
- 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
- D. 160+j75 A
- 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. 0.002 s
- 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
- B. 45
- 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
- C. Square wave
- 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
- C. 95.1 V
- 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. 0.005 s
- What is the form factor of half wave
rectified sinusoidal wave?
A. 1.57
B. 1.11
C. 1.0
D. 1.15
- A. 1.57
- 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
- B. 10.6 A
- 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)
- C. Z=R
- 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.
- D. the current lags the voltage by
90 degrees.
- Which of the following circuit
component opposes the change in the
circuit voltage?
A. Resistance
B. Inductance
C. Capacitance
D. Impedance
- C. Capacitance
- 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. a purely inductive circuit
- 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
- B. 90 A
- 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
- D. 15.7 ohms
- 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
- B. 8 A
- 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. 71.7 degrees
- 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
- B. 10 ohms
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
- D. 17.09 – j 15.4 ohms
- 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. 90.9%
- 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
- C. 32 kW
- 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
- C. 6 kVAR
- 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
- D. 20 & 10
- 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. 2000 Watts
- 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. 6.3 Amperes
- 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. 20
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
- C. 50 – j50 ohms
- In a series resonant circuit, the
impedance of the circuit is _____.
A. maximum
B. minimum
C. zero
D. approaching infinity
- B. minimum
- In a series circuit on resonance, the
following will occur except _____.
A. V=VR
B. XL=XC
C. VL=VR
D. Z=R
- C. VL=VR
- At resonance, a series RLC circuit
has
A. ω
2LC=1
B. ωLC=1
C. ωL2C=1
D. ω
2L
2C=1
- A. ω2LC=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
- C. 200 μF
- 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
- D. – j5.4
- 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
- D. 1.6 MHz
- 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. 100 Hz
- 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
- B. 3.2 ohms
- 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
- D. 41.48 lagging
- 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. 60% lagging
- 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. 2 kVAR
- 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
- C. 3,140 kVAR
- 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
- C. 174.22 μF
- 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. 155.39
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.
- D. Results into lesser voltage drop
across the lines.
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
Period
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
Root mean square (RMS)
Two relays each with 20 ohms resistance and 0.16 H inductance are connected in series. What is the equivalent impedance?
40 + j120.63
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
183 mH
5 What is the wavelength of a carrier wave with a frequency of 100 MHz?
3 m
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?
e = 325.5 sin 377t, i = 21.6 sin 377t
7 A sinusoidal current wave has a maximum value of 12.7 A. What is the average value of one-half cycle?
8.085
8 A voltage wave is given by v(t) = 100 sin 314t. How long does it take this waveform to complete one-fourth cycle?
5 ms
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?
5 Ω
10 What part of an alternating current is defined as a current which will produce the same heating effect as an equivalent direct current?
Effective value
11 The period of an ac wave is:
Equal to 1 divided by the frequency
12 If two waves have the same frequency and the same phase, the composite wave:
Has a magnitude equal to the sum of the two originals
13 A rotating vector is known as a/an ______.
phasor
14 What is the complex expression for a given alternating current, i = 15 sin (ωt – 15°)?
14.49 – j3.88
15 The average value of a symmetrical alternating quantity, (such as a sine wave), is the average value measured over a ____ cycle.
half
16 Calculate the effective value of v(t) = 100 sin 400t + 50 sin 800t + 10 cos 1200t V.
79.4V
17 Which of the following can vary with ac, but not with dc?
Frequency
18 If two waves have the same frequency and the same amplitude, but opposite phase, the composite wave is:
Zero
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?
0.001 W
20 What figure of merit describes the ratio of the maximum value and the rms value?
Peak factoR
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.
16.97 A
22 On a spectrum analyzer, a pure ac signal, having just one frequency component, would look like:
A single pip
24 An advantage of ac over dc in utility applications is:
AC is easier to transform from one voltage to another
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?
20.6 A
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.
37.9 mH
2 As the number of turns in a coil increases, the current in the coil will eventually _____.
decrease to near zero
Each impedance R – jXc:
Represents a unique combination of resistance and reactance
What is the complex expression for a given voltage equation, v = 311 cos (ωt – 15°)?
56.917 + j212.417
5 What is the average value of a half-wave rectified sinusoidal curve with maximum value of 20 V?
6.366 V
6 If R increases in an RC circuit, but Xc is always zero, then the vector in the RC plane will:
Always point straight towards the right
7 A wire carries a current, i = 3 cos 314t A. What is the average current over 6 s?
0
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.
80.311 V
9 As the number of turns in a coil increases, the reactance ______.
increases
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?
4.7 Ω
11 Each point in the RC plane:
Corresponds to a unique combination of resistance and reactance
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?
5300 rad/s
13 If the dielectric material between the plates of a capacitor is changed, all other things being equal:
You can`t say what happens to Xc without more data
14 As the size of the plates in a capacitor increase, all other things being equal:
The value of Xc decreases negatively
15 Determine the effective value of v(t) = 150 + 100 sin ωt.
165.83 V
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.
100 VAR leading
17 As the frequency of a wave gets lower, all other things being equal, the value of Xc for a capacitor ______.
increases negatively
18 In an RC circuit, as the ratio of capacitive reactance to resistance, - Xc/R, gets closer to zero, the phase angle ________.
gets closer to 0 degrees
19 As the frequency of an ac wave gets lower, the value of X_L for a particular coil _____.
decreases
20 Each point in the RL plane:
Corresponds to a unique combination of resistance and inductive reactance
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?
0.035 VA
22 Which of the following effects are generally less for an alternating current than for a direct current?
Chemical effects
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:
Get longer and rotate counterclockwise
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?
800 rad/s
25 An impedance draws a current i = 10 cos (ωt – 45°) A from a v = 220 sin ωt V. What is the apparent power?
1100 VA
