Transient Analysis EXCEL SOURCE Flashcards
- An LC resonates at 2000 kHz and has
a Q of 100. Find the lower and upper
cutoff frequencies.
A. 1950 kHz, 2050 kHz
B. 1900 kHz, 2100 kHz
C. 1990 kHz, 2010 kHz
D. 1980 kHz, 2020 kHz
- C. 1990 kHz, 2010 kHz
- If an ac-series circuit is supplied with
a source whose frequency is less than
that of fr, the circuit becomes
A. resistive
B. reactive
C. inductive
D. capacitive
- D. capacitive
- What is the magnitude of the current
at the input of a series RLC circuit as
the frequency goes through
resonance?
A. Minimum
B. Maximum
C. R/L
D. L/R
- B. Maximum
- Double-energy transients are
produced in circuits consisting of
A. two or more resistors
B. resistance and inductance
C. resistance and capacitance
D. resistance, inductance and
capacitance
- D. resistance, inductance and
capacitance
- Characteristics of the current in a
series R-L-C circuit at resonance.
A. It is dc
B. It is a minimum
C. It is zero
D. It is at maximum
- D. It is at maximum
- What is the magnitude of the
circulating current within the
components of a parallel LC circuit
at resonance?
A. It is at a minimum
B. It is at a maximum
C. It equals 1 divided by the quantity
2 times Pi, multiplied by the
square root of inductance L
multiplied by capacitance C
D. It equals 2 multiplied by Pi,
multiplied by frequency “F”,
multiplied by inductance “L”
- B. It is at a maximum
- What is the term for the time it takes
for a charged capacitor in an RC
circuit to discharge to 36.8% of its
initial voltage?
A. One discharge period
B. An exponential discharge rate of
one
C. A discharge factor of one
D. One time constant
- D. One time constant
- The shunt winding of a machine has
a resistance of 80 ohms and an
inductance of 4 H is suddenly
switched on to a 220-V supply. Find
the time taken for the current to rise
to half its steady state value.
A. 0.0346 sec C. 0.05 sec
B. 0.0251 sec D. 0.0172 sec
- A. 0.0346 sec
- Find the half-power bandwidth of a
parallel resonant circuit which has a
resonant frequency of 7.1 MHz and
Q of 150.
A. 21.1 kHz C. 47.3 kHz
B. 211 kHz D. 16.5 kHz
- C. 47.3 kH
- Given the differential equation:
di L Ri 100sin(377t)
dt
where L = 0.1 henry, R = 10 ohms
and i(0) = 0. determine the current at
t = 0.01 second.
A. 2.784 C. 2.301
B. 2.531 D. 3.062
- B. 2.531
11.Find the half-power bandwidth of a
resonant circuit which has a resonant
frequency of 1.8 MHz and a Q of 95.
A. 189 Hz C. 1.89 kHz
B. 58.7 kHz D. 18.9 kHz
- D. 18.9 kHz
- An inductor and a capacitor form a
resonant circuit. If the value of the
inductor is decreased by a factor of
four, the resonant frequency will:
A. increase by a factor of four
B. increase by a factor of two
C. decrease by a factor of two
D. decrease by a factor of four
- B. increase by a factor of two
- What is the term for the time required
for the capacitor in an RC circuit to
be charged to 63.2% of the applied
voltage?
A. An exponential rate of one
B. One time constant
C. One exponential period
D. A time factor of one
- B. One time constant
- An inductor and a capacitor are
connected in parallel. At the resonant
frequency the resulting impedance is:
A. maximum
B. minimum
C. totally reactive
D. totally inductive
- A. maximum
- What is the phase relationship
between the current through and the
voltage across a parallel resonant
circuit at resonance?
A. The voltage leads the current by
90 degrees
B. The current leads the voltage by
90 degrees
C. The voltage and current are in
phase
D. The voltage and current are 180
degrees out of phase
- C. The voltage and current are in
phase
- A “high Q” resonant circuit is one
which:
A. carries a high quiescent current
B. is highly selective
C. has a wide bandwidth
D. uses a high value inductance
- B. is highly selective
- A dc voltage E is applied across an
RL circuit at t = 0. At what time
after, is the voltage across the resistor
equal to that across the inductor?
A. 0.693 TC
B. 0.673 TC
C. 0.707 TC
D. 0.779 TC
- A. 0.693 TC
- What is the magnitude of the current
at the input of a parallel RLC circuit
at resonance?
A. Minimum
B. Maximum
C. R/L
D. L/R
- A. Minimum
- The transient current in a loss-free LC circuit when excited from an ac
source is a/an _______ sine wave.
A. Overdamped
B. Undamped
C. Under damped
D. Critically damped
- B. Undamped
- What is the resonant frequency of a
circuit when L is 50 microhenrys and
C is 10 picofarads are in parallel?
A. 3.18 MHz C. 7.12 kHz
B. 7.12 MHz D. 3.18 kHz
- B. 7.12 MHz
- An inductor and a capacitor form a
resonant circuit. The capacitor value
is increased by four times. The
resonant frequency will:
A. increase by four times
B. double
C. decrease to half
D. decrease to one quarter
- C. decrease to half
- A series RC circuit consists of R = 2
MΩ and uncharged capacitor C = 5
μF. The circuit is connected across a
10 VDC source at t = 0. What is the
initial rate of change of voltage
across the resistor?
A. – 10.0 V/s C. 10.0 V/s
B. – 12.4 V/s D. 12.4 V/s
- A. – 10.0 V/s
- What is the phase relationship
between the current through and the
voltage across a series resonant
circuit at resonance?
A. The voltage leads the current by
90 degrees
B. The current leads the voltage by
90 degrees
C. The voltage and current are in
phase
D. The voltage and current are 180
degrees out of phase
- C. The voltage and current are in phase
- An inductor and a capacitor are
connected in series. At the resonant
frequency the resulting impedance is:
A. maximum
B. minimum
C. totally reactive
D. totally inductive
- B. minimum
25.Find the Q of a circuit when the
resonant frequency is 14.128 MHz,
the inductance is 4.7 microhenrys
and the resistance is 18,000 ohms in
parallel.
A. 0.023 C. 13.3
B. 4.31 D. 43.1
- D. 43.1
A circuit whose resistance is 20 ohms inductance of 10 H has a steady-state voltage of 100 V suddenly applied to it. For the instant of 0.5 s after the voltage is applied, determine the total power input to the circuit.
200 W
There are no transients in pure resistive circuits because they ______.
have no stored energy
3 When a capacitor has been disconnected from the supply it may still be charged and it may retain this charge:
for some considerable time
4 A 1000 pF capacitor, a 1 mH inductor and a current source of i = 2 cos 10⁸t mA are in series. The capacitor voltage is zero at t = 0. Find the energy stored in the inductor at t = 0.
2 x 10¯³
5 Transient disturbance is produced in a circuit whenever:
all of the choices
6 The transients which are produced due to sudden but energetic changes from one steady state of a circuit to another are called ________ transients.
transition
7 The decay current of a coil is recorded. It is found that i_L = 10 A at t = 2 ms and i_L = 3.68 A at t = 6 ms. What is the time constant of the coil?
4 ms
8 For a decay curve, the value of a transient at a time equal to one time constant is ______ of its initial value.
0.386
9 The transient current in a loss-free L-C circuit when excited from an ac source is a/an _______ sine wave.
undamped
10 An uncharged condenser in series with a 150-V voltmeter of 20,000 ohms resistance is suddenly connected to a 120-volt battery. One second later the voltmeter reads 80 V. Calculate the capacitance of the condenser in microfarad.
123
11 A constant voltage is applied to RL circuit at t = 0. The voltage across the inductance is 20 V at t = 3.46 ms and 5 V at 25 ms. If the inductance is 2 H, what is the value of R?
128.7 ohm
12 Transient currents in electrical circuit are associated with ______.
both inductors and capacitors
13 A series circuit of resistance of 3000 ohms and a capacitor of 0.01 microfarad is suddenly connected to a 100-V battery. The capacitor has an initial stored voltage of 40 V. At this instant, at what rate is the voltage Vc charging?
2 x 10⁶ V/s
14 For a growth curve, the value of a transient at a time equal to one time constant is ______ of its steady state value.
0.632
15 The voltage across a 20-microfarad capacitor varies with time as given by v = 10.75 – 1.5e¯¹⁰⁰⁰ᵗ volts. What is the current through capacitor after 1 ms?
0.011 A
16 Double-energy transients are produced in circuits consisting of _______.
resistance, inductance and capacitance
17 The armature of a relay working on 200 V circuit operates when the current reaches 0.24 A. It is required that the relay shall close, 0.004 s after the relay circuits is closed, this time is corresponding to the time constant of the circuit. What is the inductance of the relay circuit?
2.1 H
18 A coil of 15 H inductance and 10 ohms resistance is suddenly connected to a 20-volt DC source by closing switch. The energy stored in the magnetic field 2 s after the switch is closed is:
16.3 J
19 In an R-L circuit connected to an alternating sinusoidal voltage, size of transient current primarily depends on ______.
the instant in the voltage cycle at which circuit is closed
20 The time taken for a transient to reach its final state if the initial rate of change is maintained. This is known as:
time constant
21 A capacitor has an initial charge of 8.3 C. If the current flows through it is given by the equation i = 2t + 3 A, find the charge when t = 1 s
12.3
22 In an RL transient circuit, the magnetic field energy is dissipated as ______ in the resistors and arcing at the switch contacts is avoided.
heat
23 A coil having L = 150 H, R = 200 ohms is connected in series with 100 ohms resistor. A 240-V DC source is connected to the circuit at t = 0. What is the voltage across the coil at t = 0.5 s?
88.2 V
24 A 240-V DC generator supplies current to a parallel circuit consisting of a resistor 600 ohms and a coil with resistance 300 ohms and inductance 200 H. The system is at steady state. Determine the current in the coil 5 ms after the breaker is tripped
0.78 A
25 A DC voltage of 80 V is applied to a circuit containing a resistance of 80 ohms in series with an inductance of 20 H. Calculate the growth of current at the instant completing circuit.
4 A/s
