Quiz: Electrical Engineering 21 Sep 2020

Quiz: Electrical Engineering
Exam: UPPSC-AE
Topic: Miscellaneous

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

Q1. Which of the following statement is /are correct with connection in inverters?
(a) Only CSI requires feedback diode
(b) Only VSI requires feedback diode
(c) VSI and CSI both require feedback diode
(d) None of the above

Q2. A boost regulator has an input voltage of 5V and the average output of 15 V, the duty cycle is
(a) 3/2
(b) 2/3
(c) 5/2
(d) 15/2

Q3. A microprocessor is capable of addressing 64K bytes of memory. Its address bus width is
(a) 8
(b) 16
(c) 12
(d) 20

Q4. Which of the following is correct about the gain(db.) of a cascade amplifier?
(a) Total gain(db.) is a sum of individual gains(db.)
(b) Total gain(db.) is a product of individual gains
(c) Total gain is ratio of individual gains
(d) Total gain is a product of voltage and current

Q5. In which single-phase motor, the rotor has no teeth or winding?
(a) Reluctance motor
(b) Hysteresis motor
(c) Universal motor
(d) Split phase motor

Q6. Which is the INCORRECT statement?
Unlike shell type transformers, core type transformers have
(a) A single magnetic circuit
(b) Two limbs
(c) Cylindrical or concentric winding
(d) Less losses

Q7. The series field of a short-shunt DC generator is excited by:
(a) Armature current
(b) Shunt current
(c) Load current
(d) External current

Q8. The simplified form of the Boolean expression
Y=(A ̅.B .C+D)(A ̅.D+B ̅.C ̅ ) can be written as
(a) A ̅.D+B ̅.C ̅.D
(b) A.D+B.C ̅.D
(c) (A ̅+D)(B ̅.C+D ̅ )
(d) A. D̅ + B. C. D̅

Q9. In a 220 KV system, the line to ground capacitance is 0.02 µF and capacitance is 8 H. what will be the value of resistance to be used across the contacts of the circuit breaker to eliminate the re-striking voltage if an instantaneous magnetizing current of 6 A is interrupted.
(a) 10.6 kΩ
(b) 10 KΩ
(c) 1 KΩ
(d) 100 KΩ

Q10. Which statement is true for latching current?
(a) It is related to turn off process of the device
(b) It is related to turn on process of the device
(c) It is related to conduction process of the device
(d) Both a & b

SOLUTIONS

S1. Ans.(b)
Sol. VSI v/s CSI

VSI CSI
VSI is fed from a DC voltage source having small or negligible impedance. CSI is fed with adjustable current from a DC voltage source of high impedance.
Input voltage is maintained constant The input current is constant but adjustable.
Output voltage does not dependent on the load The amplitude of output current is independent of the load.
The waveform of the load current as well as its magnitude depends upon the nature of load impedance. The magnitude of output voltage and its waveform depends upon the nature of the load impedance.
VSI requires feedback diodes The CSI does not require any feedback diodes.
The commutation circuit is complicated Commutation circuit is simple as it contains only capacitors.
Power BJT, Power MOSFET, IGBT, GTO with self-commutation can be used in the circuit. They cannot be used as these devices have to withstand reverse voltage.

S2. Ans.(b)
Sol. for boost converter: V0/VS =1/(1-α)
Where, α=duty cycle
∴15/5=1/(1-α)
∴α=1-1/3=2/3

S3. Ans.(b)
Sol. 64Kb= 64×1024 bytes=2^6×2^10=2^16 bytes
So, if A microprocessor is capable of addressing 64K bytes of memory. Its address bus width is 16.

S4. Ans.(a)
Sol. for cascaded amplifier, total gain(db.):
A_DB=A_db1+A_db2+⋯…..

S5. Ans.(b)
Sol. In hysteresis motor, the rotor has no teeth or winding.
Note: A Hysteresis Motor is a synchronous motor with a uniform air gap and without DC excitation.

S6. Ans.(d)
Sol. shell type v/s core type transformers:

Contents Core type transformer Shell type transformer
1.Circuit diagram
2.Magnetic circuit a single magnetic circuit occurs in a series form.  double magnetic circuit occurs in parallel form.
3.Winding types Concentric or Cylindrical types of windings Sandwich or Disc types of winding
4.Core limb or legs The core consists of two limbs in a single-phase transformer. The core consists of three limbs in a single-phase transformer.
5.Losses (copper and iron losses) More losses occur in core types of transformer. Fewer losses occur in shell types of transformer.

S7. Ans.(c)
Sol. Short shunt: – Here the shunt field winding is wired parallel to armature and series field winding is connected in series to the load.
The series field of a short-shunt DC generator is excited by load current.

S8. Ans.(a)
Sol. we have,
Y=(A ̅∙B∙C+D)(A ̅∙D+B ̅∙C ̅ )
=(A ̅∙B∙C∙D)+(A ̅∙B∙C∙B ̅∙C ̅ )+(A ̅∙D)+B ̅∙C ̅∙D
=A ̅∙B∙C∙D+0+A ̅∙D+B ̅∙C ̅∙D
=A ̅∙D(B∙C+1)+B ̅∙C ̅∙D
=A ̅∙D+B ̅∙C ̅∙D (∵B∙C+1=1)

S9. Ans.(b)
Sol. Resistance to be connected across the contacts to eliminate the re-striking voltage is R=0.5√(L/C)
∴ R=0.5 √(8/(0.02×10^(-6) )) = 10 KΩ.

S10. Ans.(b)
Sol. The latching current is the value of current on which the device will remain in the on state even after removal of the gate signal. Whereas, the holding current is the threshold above which the device will work.

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