# Electric Drives Questions and Answers – Electric Motors – Countercurrent Braking

This set of Electric Drives Multiple Choice Questions & Answers (MCQs) focuses on “Electric Motors – Countercurrent Braking”.

1. The value of unit step function at t=5 sec is ________
a) 0
b) 1
c) -1
d) 2

Explanation: 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 right handed and bounded signal.

2. The value of impulse at t=0 is __________
a) 0
b) 2
c) 1
d) infinite

Explanation: 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.

3. Full form of IFOC.
a) Indirect field oriented control
b) Inverter field oriented control
c) Isolated field oriented control
d) Insight field oriented control

Explanation: 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.

4. The characteristics 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

Explanation: The nature of the element is linear and bilateral. It follows the principle of homogeneity and law of additivity. For bilateral nature, it should be symmetrical in the first and third quadrant.

5. 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

Explanation: 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.
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6. Mesh analysis is only applied to the planar circuits.
a) True
b) False

Explanation: 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.

7. All loops are meshes.
a) True
b) False

Explanation: Loop is defined as the closed path which can contain small closed paths. Mesh does not contain any closed path. All meshes are loops but vice-versa is not true.

8. The nodal method is better than mesh analysis for solving circuit problems.
a) True
b) False

Explanation: 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.

9. The minimum value of the admittance in case of the parallel RLC network is ___________
a) R
b) 1÷R
c) Xl-Xc
d) Xc

Explanation: The minimum value of the admittance in case of the parallel RLC network is R. During resonance condition Xl=Xc so Y=1÷Z=(R2+(Xl-Xc)2).5=1÷R.

10. 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

Explanation: Resonance is defined as the phenomenon in which energy of any element changes from one form to another. During resonance condition Xl=Xc=2 Ω.

11. Calculate the quality factor for the resistor.
a) inf
b) 0
c) 1
d) .7

Explanation: 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.

12. Selectivity value increases for lower values of bandwidths.
a) True
b) False

Explanation: 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.

13. Calculate the equivalent resistance when two resistances are connected in parallel of values 2 Ω, 2 Ω.
a) 1 Ω
b) 2 Ω
c) 4 Ω
d) 7 Ω

Explanation: 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.

14. 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

Explanation: When two capacitances are connected in parallel their equivalent capacitance is equal to the sum of the individual capacitances. Ceq=(C1+C2)=15 F.

Sanfoundry Global Education & Learning Series – Electric Drives.

To practice all areas of Electric Drives, here is complete set of 1000+ Multiple Choice Questions and Answers. 