Quiz: Electrical Engineering

Date: 28/03/2020

Exam: NLC-GET

Topic: Miscellaneous

Each question carries 1 mark.

Negative marking: 1/4 mark

Time: 10 Minute

Q1. The SI unit of conductivity is

(a) ohm-m

(b) ohm/m

(c) mho-m

(d) mho/m

L1Difficulty 3

QTags Electrical

QCreator Devbrat Kumar

Q2. Mutual inductance between two coils can be decreased by …….

(a) increasing the number of turns of either coil

(b) moving the coils closer

(c) moving the coils apart

(d) none of the above

L1Difficulty 3

QTags Network & Circuit Theory

QCreator Devbrat Kumar

Q3. Two coupled coils with L1=L2=0.6 H have a coupling coefficient of K = 0.8. The turn ratio N1/N2 is

(a) 4

(b) 2

(c) 1

(d) 0.5

L1Difficulty 3

QTags Network & Circuit Theory

QCreator Devbrat Kumar

Q4. For balanced 3-phase supply system, the phasor sum of the line currents is NOT zero if the load is

(a)Unbalanced star connected

(b)Balanced delta connected

(c)Unbalanced delta connected

(d)Balanced star connected

L1Difficulty 3

QTags Power generation, transmission and distribution

QCreator Devbrat Kumar

Q5. The temperature rise of a transformer is directly proportional to ………

(a) apparent power

(b) reactive power

(c) leakage reactance

(d) none of the above

L1Difficulty 3

QTags Transformer

QCreator Devbrat Kumar

Q6. A load draws an active power P at a lagging p.f. of cosϕ1. If the p.f. is improved to cosϕ2,

the leading kVAR supplied by p.f. correction equipment will be

(a) P (cosϕ2-cosϕ1)

(b) P (sinϕ2-sinϕ1)

(c) P (tanϕ1+tanϕ2)

(d) P (tanϕ1-tanϕ2)

L1Difficulty 3

QTags Power generation, transmission and distribution

QCreator Devbrat Kumar

Q7. ………. increases the steady state accuracy

(a) Integrator

(b) Differentiator

(c) Phase lead compensator

(d) Phase lag compensator

L1Difficulty 3

QTags Control system

QCreator Devbrat Kumar

Q8. The transient response, with feed-back system

(a) rises slowly

(b) rises quickly

(c) decays slowly

(d) decays quickly

L1Difficulty 3

QTags Control system

QCreator Devbrat Kumar

Q9. In a 3-phase induction motor normally

(a)The rotor rotates in the direction of rotating magnetic field

(b)The rotor rotates against the direction of the rotating magnetic field

(c)The rotor rotates depending upon the supply given to it

(d)The direction of rotor rotation does not depend upon the phase sequence of the stator supply

L1Difficulty 3

QTags 3-Phase induction motor

QCreator Devbrat Kumar

Q10. The machine in which energy transfer happens both through conduction and induction, is called

(a)Three phase induction motor

(b)Single phase induction motor

(c)Auto transformer

(d)Two winding transformers

L1Difficulty 3

QTags Transformer

QCreator Devbrat Kumar

SOLUTIONS

S1. Ans.(d)

Sol. The SI unit of conductivity is mho/m

S2. Ans.(c)

Sol. Mutual inductance between two coils can be decreased by moving the coils apart.

S3. (c)

Sol. Since for a coil/inductor, the inductance

L=N²/Reluctance=N²/(l/μ0 A ) (for air core)

Or, L=(μ0 N^2 A)/l or L ∝ N²

∴ L1/L2 =(N1/N2 )^2

∴ L1/L2 =0.6/0.6=1⇒N1/N2 =1

S4. Ans. (a)

Sol. For balanced 3-phase supply if the load connected is balanced then the phasor sum of current will be zero. For unbalanced delta connected load the voltage across the load is independent of the nature of load and equal to the line voltage of the supply. For unbalanced star connected load the phasor sum of current will not be zero.

S5. Ans.(a)

Sol. The losses that occur in a transformer are (i) copper losses and (ii) iron losses. These losses

produce heat and result in the rise of temperature. Since copper loss depends upon current

and the iron loss depends upon voltage, the total loss in the transformer depends upon the

volt-ampere product only i.e. apparent power.

S6. Ans.(d)

Sol. Leading kVAR supplied = P (tanϕ1 – tanϕ2)

S7. Ans.(a)

Sol. Integrator increases the steady state accuracy.

S8. Ans.(d)

Sol. Although it is not necessary that transient response decreases everyone a feedback is applied, for e.g. take the case of positive feedback or any BIBO unstable system in negative feedback where the feedback does increases oscillations and instability. So, supposing you are talking about a BIBO stable negative feedback, the feedback produces an actuating signal that is the difference of input and feedback processed output which introduces a damping in the system, so this damping is the reason transient response decreases.

S9. Ans.(a)

S10. Ans.(c)