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DFCCIL’21 EE: Daily Practice Quiz. 15-Sep-2021

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DFCCIL’21 EE: Daily Practices Quiz

DFCCIL’21 EE: Daily Practices Quiz 15-Sep-2021

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

Q1. In a parallel resonance……….
(a) Circuit impedance is minimum
(b) Power factor is zero
(c) Line current is maximum
(d) Power factor is unity

Q2. When only current source is active in the circuit, find the current through the 10 Ω resistor.

(a) 0 A
(b) 1.66 A
(c) 0.66 A
(d) 1.33 A

Q3. 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

Q4. Choose the false statement.
(a) SCR is a bidirectional device
(b) SCR is a controlled device
(c) In SCR the gate is the controlling terminal
(d) SCR are used for high-power applications

Q5. The T vs Ia graph of a DC series motor is
(a) Straight line throughout
(b) Parabola throughout
(c) Parabola from no-load to overload
(d) Parabola up to full load and a straight line at overload

Q6. With Negative feedback……………reduces?
(a) System stability
(b) System gain
(c) Both a and b
(d) None of the above


S1. Ans.(d)
Sol. In parallel resonance condition:
Circuit impedance is maximum. Hence, current will be minimum.
Power factor unity
NOTE: For parallel resonant circuit….
Impedance is maximum
Admittance is minimum
Current is minimum
Power factor unity
Circuit is inductive below resonant frequency
Circuit is capacitive above resonant frequency

S2. Ans.(c)
Sol. When only current source is active, then replacing voltage source with equivalent resistance (R_e=0,i.e.short circuit)
∴current through 10 Ω resistor=2×(R1/(R1+R2 ))=2×(5/(5+10))=2/3=0.66 A

S3. 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.

S4. Ans.(a)
Sol. SCR is a unidirectional device, current only flows from anode to cathode.

S5. Ans.(d)
Sol. T vs I_a graph of a DC series motor:
Up to full load: T α ϕI_a or T α Ia^2 (since ϕ α Ia)
So, graph will be parabolic up to full-load.
After full-load, ? is constant due to magnetic saturation.
∴T α Ia (a straight line)


S6. Ans.(b)
Sol. Negative feedback:
Negative feedback reduces system gain and increases stability.
Increases bandwidth
Used in amplifier
Gain(Av )=G/(1+GH)
Positive feedback:
With positive feedback, overall gain of the system increases but the system may be oscillatory or unstable.
Decreases bandwidth
Used in oscillators.
Gain(Av )=G/(1-GH)

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