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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 27-Sep-2021

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

Q1. In the signal flow graph of figure y/x equals

(a) 3
(b) 2
(c) 5/2
(d) None of the above

Q2. In a salient -pole synchronous machine,
Xd= d-axis synchronous reactance
Xq= q-axis synchronous reactance
(a) Xq> Xd
(b) Xq= Xd
(c) Xq< Xd
(d) Xq=0

Q3. RC snubber circuit is used to limit the rate of
(a) Rise of current in SCR
(b) Rise of voltage across SCR
(c) Conduction period
(d) All of the above

Q4. The thyristor is turned -off when the anode current falls below_____
(a) Forward current
(b) Latching current
(c) Holding current
(d) Breakover current

Q5. In FET, the current flow is mainly due to
(a) Majority carriers
(b) Minority carriers
(c) Both a and b
(d) None of the above

Q6. The voltage across R, L and C are 3 V, 14 V and 10 V respectively as in the figure. If the voltage source is sinusoidal, then the input voltage (rms) is

(a) 10 V
(b) 5 V
(c) 2.5 V
(d) 15 V

SOLUTIONS

S2. Ans.(c)
Sol. In a salient -pole synchronous machine, X_q< X_d

S3. Ans.(b)
Sol. The thyristors can be protected against transient voltages by an RC network. This RC network is connected in parallel across the thyristor. It is called a snubber circuit.

Whenever there is a large spike or voltage transient across the thyristor, it is absorbed by the RC circuit. The RC circuit (snubber) acts as a lowpass filter for this voltage transient.

S4. Ans.(c)
Sol. latching current is associated with turn-on process and holding current that of turn-off process.
The latching current is the minimum value of anode current to trigger or turn ON the thyristor from its OFF state to ON state even after the trigger pulse is removed. To trigger an SCR, the anode current must be built up to the latching current before the gate pulse is removed.
The holding current is the minimum value of the anode current to hold the thyristor in ON state. During turn OFF, the anode current should be below the holding current.
I_holding< I_latching.

S5. Ans.(a)
Sol. A unipolar transistor is a field effect transistor (FET) that uses only one type of charge for conduction from drain to source i.e., either electrons (n-channel FET) or holes (P-channel FET).
In FET, the current flow is mainly due to majority carriers.

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