1. A circuit consists of a 3 F capacitor and a 5 H inductor. Determine the order of the circuit.
A. 2
B. 1
C. 3
D. 0
Answer: A
The order of the circuit is the number of memory/storing elements that are non-separable present in the circuit. In mathematics, the order is defined as the highest order derivate in the differential equation. The order of the circuit is 2.
2. The forced response is due to a source present in the circuit.
A. True
B. False
Answer: A
The steady-state response is a part of the forced response. The forced response is due to the electrical source present in the circuit. Its mathematical equation involves the source present in the circuit.
3. Full form of DTC.
A. Direct torque control
B. Digital torque control
C. Discrete torque control
D. Distribution torque control
Answer: A
DTC stands for Direct torque control. DTC and IFOC are the techniques used for controlling the speed and torque of a 3-phase induction motor.
4. The characteristic shown by an element in the I-V curve is V=I2. The nature of the element is _______
A. Non-linear, Bilateral, Passive
B. Linear, Unilateral, Active
C. Linear, Bilateral, Passive
D. Non-linear, Unilateral, Active
Answer: D
The nature of the element is non-linear, unilateral, and active. The shape of the characteristic is parabolic. For bilateral nature, it should be symmetrical in the first and third quadrants. Its slope is negative in the second quadrant which determines its active nature.
5. Transient response is a temporary response.
A. True
B. False
Answer: A
Transient response is a primary response in the circuit. It is a temporary response that dies out at t=infinity. It consists of exponential decaying functions.
6. Calculate the steady-state value for x(t)=4(1-e-3t).
A. 5
B. 4
C. 3
D. 2
Answer: B
The steady-state value is obtained at t=∞.
The value of x(t) at t=∞ is
4(1-e-∞)=4(1-0)=4.
The term e-3t is an exponentially decaying function.
7. The natural response is due to _________ conditions present in the circuit.
A. Initial
B. Final
C. Zero
D. Negative
Answer: A
The natural response is due to the initial conditions present in the circuit. The natural response is a complete part of the transient response. It is mathematically represented as y(t)=yo×e-at.
8. Calculate the value of the coefficient of coupling for the isolated coils.
A. 0
B. 1
C. 5
D. 7
Answer: A
The coefficient of coupling expresses how the two coils are magnetically coupled. It is mathematically represented as
K=M÷√L1.L2.
For the isolated coils, the value of the mutual inductance is 0. The value of the coefficient of coupling is 0.
9. Calculate the value of equivalent inductance for series aiding of two coils whose self inductances are 5 H, 2 H, and mutual inductance value
is 4 H.
A. 15 H
B. 12 H
C. 13 H
D. 11 H
Answer: A
The equivalent inductance for series aiding of two coils is
Leq=L1+L2+2M=5+2+8=15 H.
The value of equivalent inductance increases due to mutually induced e.m.f in the case of the magnetically coupled circuit.
10. Calculate the value of equivalent inductance for series subtracting polarity of two coils whose self inductances are 14 H, 5 H, and mutual inductance value is 1 H. [/bg_collapse]
A. 15 H
B. 17 H
C. 12 H
D. 10 H
Answer: B
The equivalent inductance for series subtracting of two coils is
Leq=L1+L2-2M=14+5-2=17 H.
The value of equivalent inductance decreases due to negatively mutually induced e.m.f in the case of the magnetically coupled circuit.
11. Calculate the value of the capacitive reactance during resonance if the value of the inductor is 5 H and the supply frequency is 20 rad/sec.
A. 100 Ω
B. 200 Ω
C. 300 Ω
D. 700 Ω
Answer: A
Resonance is defined as the phenomenon in which the energy of any element changes from one form to another. During resonance condition
Xc=Xl=ΩL=20×5=100 Ω.
55. Calculate the quality factor for the R-L circuit if R=28 Ω and L=2 H.
A. 14
B. 16
C. 10
D. 17
Answer: A
The quality factor is defined as the ratio of the reactive power to the active power consumed. The resistor always absorbs active power and the inductor absorbs the reactive power.
Quality factor=R÷L=28÷2=14.
12. The quality factor is calculated for ___________
A. Power factor loads
B. Inductive coils
C. Lagging loads
D. Leading loads
Answer: B
The quality factor is calculated for inductive coils, not for power factor loads. Its value determines the quality of the inductor or capacitor. It shows how good an inductor or capacitor can absorb reactive power.
13. Calculate the equivalent resistance when two resistances are connected in parallel of values 8 Ω, and 8 Ω.
A. 3 Ω
B. 2 Ω
C. 4 Ω
D. 7 Ω
Answer: C
When two resistances are connected in parallel their equivalent resistance is equal to the harmonic mean of the individual resistances.
Req=R1.R2÷(R1+R2)=8×8÷(8+8)=4 Ω.
14. Calculate the quality factor for the R-C circuit if R=2 Ω and C=1 F.
A. 0.2
B. 0.4
C. 0.6
D. 0.5
Answer: D
The quality factor is defined as the ratio of the reactive power to the active power consumed. The resistor always absorbs active power and the capacitor absorbs the reactive power.
Quality factor=1÷RC=1÷2=.5.
15. Power input to an induction motor is given by _________
A. 3VpIpcosΦ
B. 2VpIpcosΦ
C. VpIpcosΦ
D. 5VpIpcosΦ
Answer: A
Power input to a 3-Φ induction motor is 3VpIpcosΦ. The power remains the same for Delta and star connections. The power is constant and has no vibrations.
16. For motoring mode, the phase angle between the stator phase voltage and stator phase current should be _______
A. < 90°
B. > 90°
C. < 40°
D. 180°
Answer: A
For motoring mode, the phase angle between the stator phase voltage and stator phase current should be < 90°. The rotor magnetic field tries to catch up with the stator magnetic field.
17. The relative speed between the stator magnetic field and rotor in the induction motor is ______
A. Ns
B. Ns-Nr
C. Ns+Nr
D. 0
Answer: B
In induction motor rotor tries to catch up with the stator magnetic field in order to satisfy Lenz law. Effect opposes the cause. Stator magnetic field rotates at the speed of synchronous speed.
18. The relative speed between the stator magnetic field and rotor in the synchronous generator is ______
A. Ns
B. Ns-Nr
C. Ns+Nr
D. 0
Answer: D
In a synchronous generator rotor and stator magnetic field rotates at speed of synchronous speed in order to produce the steady-state torque.
19. The relative speed between the stator magnetic field and stator in the induction motor is ______
A. Ns
B. Ns-Nr
C. Ns+Nr
D. 0
Answer: A
In Induction motor stator magnetic field rotates at the speed of synchronous speed. The stator is made up of Silicon steel and remains at rest. The relative speed is Ns-0 = Ns.
20. The relative speed between the rotor and stator in the induction motor is ______
A. Nr
B. Ns-Nr
C. Ns+Nr
D. 0
Answer: A
In Induction motor rotor tries to catch up with the stator magnetic field in order to satisfy Lenz law. Effect opposes the cause. The stator remains at rest.
