NHPC-JE'21 EE: Daily Practices Quiz 15-NOV-2021

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NHPC-JE’21 EE: Daily Practices Quiz

NHPC-JE’21 EE: Daily Practices Quiz 15-NOV-2021

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 06 min.

Q1. …… at a point due to a charge distribution is the work done per unit charge when it is
moved from infinity to that point.
(a) Electric current
(b) Resistance
(c) Potential
(d) Conductivity

Q2. Which of the following is the property of an ideal operational amplifier?
I. It should have an infinite input impedance.
II. It should have a zero-output impedance.
(a) Only I
(b) Only II
(c) Both I and II
(d) Neither I nor II

Q3. A transmission line is distortion less if
(a) RL = 1/RC
(b) RL = GC
(c) GL = RC
(d) RL = LC

Q4. Standstill impedance of an induction motor is (0.08+j 0.4) Ω. Slip at which it will produce maximum torque is:
(a) 0.32
(b) 0.032
(c) 0.2
(d) 0.48

Q5. The insulating material for a cable should have
(a) Low cost
(b) High dielectric strength
(c) High mechanical strength
(d) All of the above

Q6. A single-phase transformer with a 2-kVA rating has a 480-V primary and a 120-V secondary. Determine the primary and secondary full-load currents of the transformer.
(a) 4.17 A and 16.67 A
(b) 10 A and 13. 2 A
(c) 6 A and 16.67 A
(d) Insufficient Data

SOLUTIONS

S1. Ans.(c)
Sol. Electric potential at a point in an electric field is defined as the work done in bringing a unit positive charge from infinity to that point.
Or, V= W/q.

S2. Ans.(c)
Sol. Characteristics of an ideal op-amp:
Infinite open loop voltage
Infinite input resistance
Zero output resistance
Infinite bandwidth
Infinite common-mote rejection ratio (CMRR)

S3. Ans.(c)
Sol. A transmission line is said to be DISTORTIONLESS if attenuation constant ‘α’ is frequency independent and the phase shift constant ‘β’ is linearly dependent on the frequency.
The condition is – GL = RC
⇒L/C=R/G

S4. Ans.(c)
Sol. At maximum torque slip is, s_m=R_2/X_2 =0.08/0.4=0.2.

S5. Ans.(d)
Sol. The insulating materials used in cables should have the following properties
High insulation resistance to avoid leakage current.
High dielectric strength to avoid electrical breakdown of the cable.
High mechanical strength to withstand the mechanical handling of cables.
Non-hygroscopic, that is, it should not absorb moisture from air or soil.
Non-inflammable.
Low cost so as to make the underground system a viable proposition.
Unaffected by acids and alkalis to avoid any chemical action.

S6. Ans.(a)
Sol. Primary full-load current = VA rating / Primary Voltage
Primary full-load current = (2 * 1 000) / 480 V = 4.17 A
Secondary full-load current = VA rating / Secondary Voltage
Secondary full-load current = (2 * 1 000) / 120 V = 16.67 A