UPPSC-LECTURER'21 EE: Daily Practices Quiz 16-NOV-2021

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UPPSC polytechnic lecturer QUIZ: EE

UPPSC-LECTURER’21 EE: Daily Practices Quiz 16-NOV-2021

Each question carries 3 marks.
Negative marking: 1 mark each or 1/3rd
Total Questions: 06
Time: 08 min.

Q1. In JK flip flop, the race round condition takes place when:
(a) J = 0, K = 0
(b) J = 0, K = 1
(c) J = 1, K = 0
(d) J = 1, K = 1

Q2. A 50 Hz, 3- phase synchronous generator has inductance per phase of 15 mH. The capacitance of generator and circuit breaker is 0.002 µF. What is its natural frequency of oscillations?
(a) 29 MHz
(b) 29 kHz
(c) 2.9 kHz
(d) 290 kHz

Q3. A 6-pole dc armature has simplex lap-connected 720 conductors, 3 turns per coil and 4 coil-sides per slot. Determine the number of slots in the armature and state whether equalizers can be employed or not.
(a) 30 slots and possible
(b) 30 slots and not possible
(c) 60 slots and possible
(d) 60 slots and not possible

Q4. An IGBT is a combination of…
(a) SCR and MOSFET
(b) UJT and MOSFET
(c) BJT and MOSFET
(d) None of the above

Q5. Which of the following Boolean algebra rules is NOT correct?
`(a) A.A ̅=0
(b) A+A ̅=1
(c) A+AB=A+B
(d) A+A ̅B=A+B

Q6. What is the value of charging current in short transmission lines?
(a) Less than medium transmission lines
(b) Equal to medium transmission lines
(c) More than medium transmission lines
(d) More than long transmission lines

SOLUTIONS

S1. Ans.(d)
Sol. In JK flip flop, race round condition takes place when J = 1, K = 1.
When J = K = 1, at each clock pulse output changes (toggles) without any change in the input, is known as Race a round condition.
NOTE:
This problem (Race Around Condition) can be avoided by ensuring that the clock input is at logic “1” only for a very short time.
This introduced the concept of Master Slave JK flip flop.

S2. Ans.(b)
Sol. f_r=1/(2π√LC)=1/(2π√(15×10^(-3)×2×10^(-9) ))=10^6/34.39≃29×10^3=29 kHz.

S3. Ans.(c)
Sol. Each coil has 2 coil side.
∴total turn in per slot=4/2 ×3=6
Each turn has 2 conductors.
∴number of conductors/slots=12
∴total no. of conductors=no. of slots× no. of conductors per slot
⇒720=no.of slot×12
∴ no. of slots=720/12=60
Equalizer ring is used for lap connection.

S4. Ans.(c)
Sol. An IGBT is a combination of BJT and MOSFET.
IGBT is a bipolar device.
It has high switching frequency.
Low conduction loss.

S5. Ans.(c)
Sol. As per property:
A.A ̅=0
A+A ̅=1
A+AB=A(1+B)=A
A+A ̅B=(A+A ̅ )(A+B)=A+B

S6. Ans.(a)
Sol. Line to Earth capacitance of short transmission line is less than that in medium and long transmission line and is negligible. Because of this the charging current of short transmission line is less than that in medium and long transmission line and is negligible.