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# DFCCIL Recruitment 2021

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## EXAM DATES

26 SEPT TO 30 SEPT

## DFCCIL’21 EE: Daily Practices Quiz

DFCCIL’21 EE: Daily Practices Quiz 24-Sep-2021

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 08 min.

Q1. A GTO can be turned off by:
(a) Removing gate signal
(b) Positive gate signal
(c) Negative gate signal
(d) None of the above

Q2. Zener diode is usually operated
(a) In forward bias mode
(b) In reverse bias mode
(c) Near cut-in voltage
(d) In forward linear region

Q3. Derivative controller improves the stability by:
(b) Reducing settling time
(c) Reducing oscillations
(d) Increasing peak overshoot

Q4. If x(t)=t^n u(t), then the Laplace transform of x(t) is:
(a) nǃ/s^(n+1)
(b) nǃ/s^n
(c) n/s^(n+1)
(d) nǃ/s^(n-1)

Q5. For the given switch circuit, taking open as 0 and closed as 1 the expression for the circuit is Y then Y is given by

(a) A + (B + C) D
(b) A + BC + D
(c) A (BC + D)
(d) None of these

Q6. The pull-out torque of a salient pole synchronous motor occurs when the torque angle is about
(a) 0°
(b) 90°
(c) 30°
(d) 75°

## SOLUTIONS

S1. Ans.(c)
Sol. Gate turn-off thyristor is an advancement of the conventional thyristor. A GTO is designed in a way that it can be turned on by the application of a positive gate pulse at the terminal as well as can be turned off when a negative gate current is applied at its terminal.

S2. Ans.(b)
Sol. Zener diode is usually operated in reverse bias mode.

S3. Ans.(b)
Sol. Derivative controller:
Reduces rise time and settling time
Increases bandwidth
Improves transient response
Increase input noise
Improves stability
Improves GM, PM

S4. Ans.(a)
Sol. L[t^n u(t)]=nǃ/s^(n+1)

S5. Ans(c)
Sol. We know that Switch in Parallel is indicated by ‘+’ (OR gate) and Switch in series is indicated by (.) or (And gate).
Now, Output is available when switch A is always closed while either both switch B and C are closed or Only switch D is closed. So, we get
Y = A. (BC + D)

S6. Ans.(d)
Sol. The maximum torque is pull out torque it will occur at Ө= 90°, But this is possible for the motor having smooth rotors. As most practical motors have salient poles, so the pull-out torque occurs at a torque angle about to 75°.

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