Quiz: Electrical Engineering 05 July 2021

Quiz: Electrical Engineering
Exam: DFCCIL
Topic: Miscellaneous

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. In the circuit shown in the Fig. R_Th equals

(a) R3+((R1×R2))/(R1+R2 )
(b) R1+((R2×R3))/(R2+R3 )
(c) R2+((R3×R1))/(R3+R1 )
(d) none of the above

Q2. For maximum transfer of power, internal resistance of the source should be
(a) equal to load resistance
(b) less than the load resistance
(c) greater than the load resistance
(d) none of the above

Q3. Superposition theorem may be applied only to circuit elements which are-
(a) Non-linear
(b) Linear – bilateral
(c) Passive
(d) none of the above

Q4. Which of the following speed control method of a DC machine is NOT a constant torque drive?
(a) Armature resistance control
(b) Armature voltage control
(c) Field flux control
(d) All of the above

Q5. In a transformer the voltage regulation will be zero when it operates at:
(a) Lagging pf
(b) Leading pf
(c) Unity pf
(d) Zero pf leading

Q6. In ACSR conductors, steel is used for:
(a) compensating skin effect
(b) neutralizing proximity effect
(c) reducing line inductance
(d) increasing the tensile strength

Q7. A synchronous motor working at leading power factor can be used as
(a) Current booster
(b) Voltage booster
(c) Power factor correction
(d) All of the above

Q8. Earth wire on EHV overhead transmission line is provided to protect the line against:
(a) Lightning surge
(b) Switching surge
(c) Excessive fault voltage
(d) Corona effect

Q9. The diode used for voltage regulator is
(a) Zener diode
(b) Schottky diode
(c) Varactor diode
(d) Tunnel diode

Q10. The Maxwell’s Inductance-Capacitance bridge is not suitable for the measurement inductance of coil if the Q factor is
(a) Less than 1
(b) Between 1 to 10
(c) More than 10
(d) Both (a) and (c)

SOLUTIONS

S1. Ans.(a)
Sol. For calculation of R_Th the voltage source will get short circuited and R_Th will be calculated by removing load resistance (R_L).

R_1 and R_2 are in parallel and total resistance obtained is in series with R_3.
Therefore, RTh = R3+((R1×R2))/(R1+R2 )

S2. Ans.(a)
Sol. According to Maximum Power Transfer theorem, the maximum external power from a source with a finite internal resistance can be obtained if the resistance of the load must be equal to the resistance of the source.

S3. Ans.(b)
Sol. Superposition theorem not applicable for: –
Non – linear or power signal
Unilateral elements such as diode, BJT
Passive elements

S4. Ans.(c)
Sol. Field flux control is constant power drive.

S5. Ans.(b)
Sol. In a transformer the voltage regulation will be zero when it operates at leading pf.

(VR=(%R)cosϕ\ ±(%X)sinϕ)

  • → for lagging
  • → for leading
    Maximum regulation at lagging pf
    Minimum or zero or negative regulation at leading pf

S6. Ans.(d)
Sol. ACSR stands for aluminium conductor steel reinforced and steel is used for increasing the tensile strength.

S7. Ans.(c)
Sol. An over-excited synchronous motor has a leading power factor. This makes it useful for power factor correction of industrial loads. If DC field excitation of a synchronous motor is such that back EMF Eb is greater than applied voltage V, then the motor is said to be over excited. An over excited synchronous motor draws leading current.

S8. Ans.(a)
Sol. Earth wire on EHV overhead transmission line is provided to protect the line against
lightning surge.

S9. Ans.(a)
Sol. Zener diode is used to regulate the voltage level. It generates a fixed output voltage that remains constant for any changes in load conditions or input voltage.

S10. Ans.(d)
Sol. The Maxwell’s Inductance-Capacitance bridge is not suitable for the measurement inductance of coil if the Q factor is (110.
For Q<1: Anderson bridge For Q>10: Hay bridge

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