DFCCIL’21 EE: Daily Practices Quiz 14-July-2021

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

Q1. An RLC series circuit has R = 10 , L = 2 H. What value of capacitance will make the circuit critically damped?
(a) 0.02 F
(b) 0.08 F
(c) 0.2 F
(d) 0.4 F

Q2. According to Thevenin’s theorem, any bilateral network can be replaced by a network with—
(a) An independent current source in parallel to the equivalent resistance
(b) An independent voltage source in series with the equivalent resistance
(c) An independent voltage source in parallel to the resistance
(d) None of these

Q3. In case of power transformer
(a) Positive, negative and zero- sequence impedances all are equal
(b) Positive and negative sequence impedances are equal but less than zero sequence impedance.
(c) Positive sequence impedance is greater than both negative and zero sequence impedances.
(d) Positive sequence impedance is less than negative sequence impedance but equal to zero sequence impedance.

Q4. The maximum short-circuit current occurs in the case of
(a) A line-to-line fault
(b) A single line to ground fault
(c) A three-phase fault
(d) A double line to ground fault

Q5. For the circuit shown in the figure, the voltage across the capacitor during the steady-state condition is

(a) 0 V
(b) 4 V
(c) 6 V
(d) 12 V

Q6. Hard magnetic materials are used for manufacturing ……
(a) Insulators
(b) Temporary magnets
(c) Permanent magnets
(d) Conductors

SOLUTIONS
S1. Ans.(b)
Sol. For RLC series circuit, condition for critical damping:
(R/2L)^2=1/LC⇒R^2=4L/C
In an RLC series circuit, for critically damped:〖 R〗^2=4L/C
C=4L/R^2 =(2×4)/100=0.08 F

S2. Ans.(b)
Sol. Thevenin’s equivalent consists of independent voltage source in series with resistance.

S3. Ans.(b)
Sol. For power transformer,Z_1=Z_2 and Z_0>Z_1
Z_1=positive sequence impedance
Z_2= negative sequence impedance
Z_0= zero sequence impedance

S4. Ans.(c)
Sol. A three-phase fault is most severe and having highest value of shot-circuit current.

S5. Ans.(d)
Sol. in steady state condition, capacitor acts as open circuit. So, in steady-state condition, the voltage across the capacitor equals the voltage of the charging source i.e., 12 V.

S6. Ans.(c)
Sol. Hard magnets, also referred to as permanent magnets, are magnetic materials that retain their magnetism after being magnetised. It is used for manufacturing permanent magnets.
Permanent magnets are difficult to magnetise as unlike magnetically soft materials their atomic magnetic domains aren’t easily aligned but once they are aligned, they remain so indefinitely.

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