111. 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.
112. 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.
113. 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.
114. 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.
115. 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.
116. 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.
117. 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.
118. 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.
120. The value of unit step function at t=5 sec is ________
A. 0
B. 1
C. -1
D. 2
Answer: B
The unit step function is discontinuous at t=0.
The value of the unit step function is 1
for t>0 and zero for t<0.
It is a right-handed and bounded signal.
122. The value of impulse at t=0 is __________
A. 0
B. 2
C. 1
D. infinite
Answer: D
The impulse function is neither an energy signal nor a power signal. It is a pulse of infinite amplitude and zero width. The value of impulse is 0 for time not equal to zero.
123. Full form of IFOC.
A. Indirect field-oriented control
B. Inverter field-oriented control
C. Isolated field-oriented control
D. Insight field-oriented control
Answer: A
IFOC stands for indirect field-oriented control. DTC and IFOC are the techniques used for controlling the speed and torque of a 3-phase induction motor.
124. The characteristic shown by an element in the I-V curve is a straight line passing through the origin with a positive slope. The nature of the element is _______
A. Non-linear, Bilateral
B. Linear, Unilateral
C. Linear, Bilateral
D. Non-linear, Unilateral
Answer: C
The nature of the element is linear and bilateral. It follows the principle of homogeneity and the law of additivity. It should be symmetrical in the first and third quadrant for bilateral nature.
125. Calculate the total energy stored in the inductor if the current value is 4 A and inductance values are 1 H and 2 H.
A. 72 J
B. 22 J
C. 82 J
D. 24 J
Answer: D
The energy stored in the inductor is
.5×Leq×I2.
The value of Leq=1+2=3 H.
The total amount of energy stored in the inductor in the steady-state condition.
E=.5×eq×I2
=.5×3×4×4=24 J.
126. Mesh analysis is only applied to the planar circuits.
A. True
B. False
Answer: A
The mesh analysis is one of the network tools to find the responses in the circuits. It is only applicable to planar circuits. Planar circuits are 2-D circuits as mesh analysis involves mesh circulating currents.
127. All loops are meshes.
A. True
B. False
Answer: B
Loop is defined as a closed path that can contain small closed paths. Mesh does not contain any closed path. All meshes are loops but vice-versa is not true.
128. The nodal method is better than mesh analysis for solving circuit problems.
A. True
B. False
Answer: A
The nodal method is one of the best methods to solve any circuit problem. It is based on the KCL equation. It is applicable for planar and non-planar circuits. Mesh analysis cannot be applicable for non-planar circuits.
129. The minimum value of the admittance in the case of the parallel RLC network is ___________
A. R
B. 1÷R
C. Xl-Xc
D. Xc
Answer: B
The minimum value of the admittance in the case of the parallel RLC network is R. During resonance condition
Xl=Xc
so
Y = 1÷Z = (R2+(Xl-Xc)2).5 = 1÷R.
130. Calculate the value of the inductive reactance during resonance if the value of capacitive reactance is 2 ohm.
A. 8 Ω
B. 2 Ω
C. 3 Ω
D. 1 Ω
Answer: B
Resonance is defined as the phenomenon in which the energy of any element changes from one form to another.
During resonance condition Xl=Xc=2 Ω.
131. Calculate the quality factor for the resistor.
A. inf
B. 0
C. 1
D. .7
Answer: B
The quality factor is defined as the ratio of the reactive power to the active power consumed. The resistor always absorbs active power. The value of reactive power consumed is 0.
Quality factor=0/P=0.
132. Selectivity value increases for lower values of bandwidths.
A. True
B. False
Answer: A
Bandwidth is defined as the range of frequencies for which the signal exists. Selectivity is inversely proportional to the bandwidth. Lower the bandwidth lower will be the cost.
133. Calculate the equivalent resistance when two resistances are connected in parallel of values 2 Ω, and 2 Ω.
A. 1 Ω
B. 2 Ω
C. 4 Ω
D. 7 Ω
Answer: A
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)=22 Ω.
134. Calculate the equivalent capacitance when two capacitors are connected in parallel of values 8 F, 7 F.
A. 15 F
B. 20 F
C. 40 F
D. 7 F
Answer: A
When two capacitances are connected in parallel their equivalent capacitance is equal to the sum of the individual capacitances.
Ceq=(C1+C2)=15 F.
135. Plugging is suitable for __________ type loads.
A. Gravitational
B. Electrostatic
C. Weightless
D. Leading
Answer: A
Plugging is suitable for gravitational type loads. It halts the motor operation. It can reverse the direction of rotation of the motor. It can hold the motor at zero speed.
136. In DC shunt machine ∅ is directly proportional to Ia.
A. True
B. False
Answer: B
In a shunt DC machine, the field winding is in parallel with the armature winding. The armature current flows through the armature winding.
IF∝∅∝Vt.
137. Braking resistance should be selected in order to limit the braking current.
A. True
B. False
Answer: A
During braking, a high current flows in the armature circuit. To limit the braking current a proper value of braking resistance should be selected.
138. Torque developed in the motor is ___________
A. KmΦIa
B. KmΦIa3
C. 2KmΦIa
D. KmΦIa2
Answer: A
The torque developed in the motor is directly proportional to the flux, machine constant, and armature current. It is mathematically represented as
T= KmΦIa.
139. Full form of TVR is _________
A. Terminal voltage reversal
B. Total voltage reversal
C. Terminal voltage redirect
D. Total voltage reversal
Answer: A
TVR stands for terminal voltage reversal. It is one of the methods of countercurrent braking of the DC shunt motor. It halts the motor rapidly and reverses its direction of rotation.
130. Calculate the current in DC shunt field winding using the following data: Ia=15 A, IL=21, R=22, N=484.
A. 4 A
B. 2 A
C. 7 A
D. 6 A
Answer: D
In the DC shunt motor, field windings are connected in parallel with the armature circuit.
IF=IL-Ia=11-5=6 A.
Motor current is the sum of field and armature current.
