Quiz: Electrical Engineering 19 Apr 2021

Quiz: Electrical Engineering
Topic: Miscellaneous

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

Q1. Which of the following features are offered by a bipolar junction transistor amplifier in Darlington connection?

  1. High current gain
  2. High voltage gain
  3. High input impedance
    Select the correct answer using the code given below:
    (a) 1 and 2 only
    (b) 2 and 3 only
    (c) 1 and 3 only
    (d) 1, 2 and 3

Q2. The application of a CC configured transistor is_________
(a) voltage multiplier
(b) level shifter
(c) rectification
(d) impedance matching

Q3. In 3-phase induction motor maximum torque is inversely proportional to the
(a) Speed of rotor
(b) Stator voltage
(c) Decreasing slip speed
(d) Rotor reactance

Q4. A centrifugal switch is provided for disconnecting the auxiliary winding in a
(a) Capacitor start motor
(b) Capacitor run motor
(c) Hysteresis motor
(d) Reluctance motor

Q5. The ratio of primary to secondary voltages is 2:1. The saving in terms of weight of copper required if an autotransformer is used instead of a two-winding transformer will be:
(a) 33.3 %
(b) 50 %
(c) 66.7 %
(d) 95 %

Q6. If the conductor radius increases, inductance of the line-
(a) increases
(b) decreases
(c) remains same
(d) may increase or decrease

Q7. Voltage regulation of a transmission line should be __
(a) Minimum
(b) Maximum
(c) Greater than 50 %
(d) Less than 50 %

Q8. When the supply frequency is more than the resonant frequency in a parallel a.c.
circuit, then circuit is…….
(a) Resistance
(b) capacitive
(c) inductive
(d) none of the above

Q9. A dc series motor drawing an armature current of I_a is operating under saturated magnetic conditions, torque developed in the motor is proportional to
(a) 1/Ia
(b) 1/Ia^2
(c) Ia^2
(d) Ia

Q10. Fusing factor of fuse is always
(a) More than 1
(b) Less than 1
(c) Infinity
(d) Zero

S1. Ans.(c)
Sol. The Darlington Transistor consists of two PNP transistors or NPN transistors connected back-to-back. It is primarily used because it offers a particularly high current gain and this also reflects into a high input impedance for the overall Darlington circuit when compared to a single transistor.
The Darlington Transistor offers:
High input impedance
High current gain(i.e.Ai=β1 β2)

S2. Ans.(d)
Sol. Applications of Common-collector or Emitter-follower:
used as an impedance matching circuit.
It is used as a switching circuit.
The high current gain combined with near-unity voltage gain makes this circuit a great voltage buffer
It is also used for circuit isolation.

S3. Ans.(d)
Sol. In 3-phase induction motor: T_(max ) α 1/X_2

S4. Ans.(a)
Sol. In case of capacitor start motor, a centrifugal switch is provided for disconnecting the auxiliary winding when the motor attains speed up-to 70-80% of synchronous speed.

S5. Ans.(b)
Sol. Here, a=2
∴ Cu saving=1/a=1/2=0.5=50%

S6. Ans.(b)
Sol. Inductance of a line.
L = 2×10-7 ln[GMD/GMR] H/m/phase
and. GMR α Radius of the conductor
If radius increases then GMR will increase and inductance will decrease.

S7. Ans.(a)
Sol. More value of voltage regulation means more voltage fluctuations and this is undesirable. So, the value of voltage regulation should be as low as possible.

S8. Ans.(b)
Sol. Capacitive

S9. Ans.(d)
Sol. We know Torque Tα Φ Ia, As the motor is operating under saturation condition so torque will be independent of flux i.e., T α Ia.

S10. Ans.(a)
Sol. Fusing factor=(minimum fusing current)/(current rating of fuse)
Fusing factor of fuse is always >1.


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