11. Calculate the quality factor for the pure capacitor.
A. inf
B. 0
C. 1
D. 2
Answer: A
The quality factor is defined as the ratio of the reactive power to the active power consumed. The pure capacitor always absorbs reactive power. The value of active power consumed is 0.
Quality factor=Q/0=inf.
12. Calculate the equivalent inductance when n inductors are connected in a series of values L.
A. n2L H
B. nL H
C. .5L H
D. 2 H
Answer: B
When two inductors are connected in series their equivalent inductance is equal to the sum of the individual inductances.
Leq=L+L+…..+n times L=nL H.
13. Calculate the equivalent resistance when two resistances are connected in a series of values 12 Ω, and 10 Ω.
A. 32 Ω
B. 22 Ω
C. 47 Ω
D. 17 Ω
Answer: B
When two resistances are connected in series their equivalent resistance is equal to the sum of the individual resistances.
Req=R1+R2=22 Ω.
14. Reactive power is positive in the case of the inductor.
A. True
B. False
Answer: A
The reactive power is defined as the product of the voltage, current, and sine of the difference between the phase angle of voltage and current. In the case of an inductor, the voltage leads to the current. The value of sine is positive and reactive power is positive.
15. Reactive power is positive in the case of the capacitor.
A. True
B. False
Answer: B
The reactive power is defined as the product of the voltage, current, and sine of the difference between the phase angle of voltage and current. In the case of a capacitor, the voltage lags the current. The value of sine is negative and reactive power is negative.
16. Which braking method is the best method for obtaining high braking torque?
A. Regenerative braking
B. Plugging
C. Dynamic braking
D. Rheostatic braking
Answer: B
Plugging is the best braking method among all braking techniques. In plugging the value of the armature current reverses and the mechanical energy is extracted. A very high braking torque is produced in the case of plugging.
17. The polarity of back e.m.f changes in which of the method?
A. Plugging
B. Regenerative braking
C. Dynamic braking
D. Rheostatic braking
Answer: A
In the case of the Plugging braking technique polarity of the back e.m.f voltage changes due to which current direction changes and mechanical, and electrical energy are wasted in the form of heat in resistors.
18. Full form of WRIM.
A. Wound round induction motor
B. World cage induction motor
C. Wolf cage induction motor
D. Squirrel cage inverter motor
Answer: A
WRIM stands for wound round induction motor. WRIM rotor is made up of armature conductors. There are no copper bars or rods involved in it.
19. Calculate the energy stored in the capacitor if the voltage across the capacitor is 20 V and the capacitance value is 2 F.
A. 400 J
B. 200 J
C. 100 J
D. 50 J
Answer: A
The energy stored in the capacitor is .5×C×V2. It is the total amount of energy stored in the capacitor in the steady-state condition.
E=.5×C×V2
=.5×2×20×20=400 J.
20. Calculate the energy stored in the inductor if the current value is 4 A and the inductance value is 1 H.
A. 4 J
B. 2 J
C. 8 J
D. 5 J
Answer: C
The energy stored in the inductor is .5×L×I2. It is the total amount of energy stored in the inductor in the steady-state condition.
E=.5×L×I2
=.5×1×4×4=8 J.
21. All networks are always circuits.
A. True
B. False
Answer: B
The network is defined as the interconnection of electrical elements that may or may not has a closed path. The circuit is defined as the interconnection of an element that must have at least one closed path. All networks are not always circuits but vice-versa is true.
22. The Thevenin voltage of a dead circuit is zero volts.
A. True
B. False
Answer: A
In the case of the dead network, there are no independent sources available in the electrical circuit. The Thevenin voltage of the circuit is zero because no force is available to drive the current in the circuit.
23. During the open circuit condition, the current is equal to ______
A. 1 A
B. 0 A
C. 4 A
D. 7 A
Answer: B
During the open circuit condition, the current is equal to zero amperes.
According to Ohm’s law, I=V/R=0 A.
The value of the voltage can be positive, negative, or zero.
24. The minimum value of the impedance in the case of the series RLC network is ___________
A. R
B. 0
C. Xl
D. Xc
Answer: A
The minimum value of the series impedance in the case of the series RLC network is R. During resonance condition
Xl=Xc
Z=(R2+(Xl-XC)2).5=R.
25. Calculate the quality factor for the purely inductive coil.
A. inf
B. 10
C. 3
D. 6
Answer: A
The quality factor is defined as the ratio of the reactive power to the active power consumed. The purely inductive coil always absorbs reactive power. The value of active power consumed is 0.
Quality factor=Q/0=inf.
26. Speed of DC shunt motor is directly proportional to___________
A. Eb
B. Φ
C. Vt
D. Ia.Ra
Answer: A
The back e.m.f in case of DC shunt motor is Eb=Vt-Ia.Ra.
The speed in the DC shunt motor is
Eb÷Kv.
The speed is directly proportional to Eb.
27. Calculate the value of the angular acceleration of the DC shunt motor using the given data: J = 1 kg-m2, load torque = 1 N-m, motor torque = 2 N-m.
A. 1 rad/s2
B. 2 rad/s2
C. 3 rad/s2
D. 5 rad/s2
Answer: A
Using the dynamic equation of motor J×(angular acceleration)
= Motor torque – Load torque: 1×(angular acceleration)
= 2-1=1, angular acceleration=1 rad/s2.
28. Calculate the quality factor for the R-L circuit if R=16 Ω and XL=8 Ω with a supply frequency is 1 rad/sec.
A. 2
B. 6
C. 0
D. 7
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.
ΩL=8, L=8 Henry
quality factor=R÷L
=16÷8=2.
29. Calculate the equivalent resistance when two armature resistances are connected in parallel of values 6 Ω, 3 Ω.
A. 3 Ω
B. 2 Ω
C. 4 Ω
D. 7 Ω
Answer: B
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)
=6×3÷(6+3)=2 Ω.
30. Calculate the quality factor for the R-C circuit if R=1 Ω and C=1 F.
A. 2
B. 4
C. 1
D. 5
Answer: C
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.
