Quiz: Electrical Engineering 11 Mar 2021

Quiz: Electrical Engineering
Exam: UPPCL-JE
Topic: Miscellaneous

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. Quadrature axis synchronous reactance is the ratio of….
(a) (V(max ) )/Imax
(b) Vmax/Imin
(c) Vmin/Imax
(d) Vmin/Imin

Q2. Direct axis synchronous reactance is the ratio of……
(a) (V(max ) )/Imax
(b)Vmax/Imin
(c) Vmin/Imax
(d) Vmin/Imin

Q3. In which of the following conditions will a 3-phase synchronous machine works as a capacitor?
(a) Over excited
(b) Under excited
(c) Critically excited
(d) None of the above

Q4. A 4-pole, 50 Hz induction motor operates at 5 % slip. The frequency of emf induced in the rotor will be
(a) 50 Hz
(b) 25 Hz
(c) 2 Hz
(d) 2.5 Hz

Q5. Slip of an induction motor ……………. when the rotor starts gaining speed.
(a) Increases
(b) Decreases
(c) Remains same
(d) Increase or decrease

Q6. Current chopping usually occurs in
(a) Oil circuit breaker
(b)Minimum OCB
(c) MCB
(d) Air blast circuit breaker

Q7. A coil of resistance 10 Ohms and inductance 10 mH is connected in a series with a 0.01 mF capacitor. Find the value of current (in A) at resonance, if the circuit is connected across 10 V supply.
(a) 10
(b) 1
(c) 14.14
(d) 1.414

Q8. In an R-C-L series circuit, during resonance, the impedance will be ………….
(a) Zero
(b) Minimum
(c) Maximum
(d) None of these

Q9. Reciprocal of resistance is called
(a) Impedance
(b) Conductance
(c) Inductance
(d) Susceptance

Q10. Two electric bulbs of 50 w and 100w are connected in series to mains. Which of the two bulbs will glow brighter?
(a) 50W
(b) 100W
(c) Both 50W and 100W
(d) None of theses

SOLUTIONS

S1. Ans.(c)
Sol. Quadrature axis synchronous reactance: Xq=Vmin/Imax
Direct axis synchronous reactance: Xd=Vmax/Imin

S2. Ans.(b)
Sol. Quadrature axis synchronous reactance: Xq=Vmin/Imax
Direct axis synchronous reactance: Xd=Vmax/Imin

S3. Ans.(a)
Sol. Over excited synchronous machine behaves as capacitor and provide reactive power.

S4. Ans.(d)
Sol. The frequency of emf induced in the rotor: fr=sf=0.05×50=2.5 Hz

S5. Ans.(b)
Sol. Slip(s)=(Ns-Nr)/Ns
So, when the rotor starts gaining speed, due to increase of rotor speed, slip of an induction
motor decreases.

S6. Ans.(d)
Sol. Current chopping usually occurs in Air blast circuit breaker.
Current Chopping in circuit breaker is defined as a phenomenon in which current is forcibly interrupted before the natural current zero.

S7. Ans.(b)
Sol. In case of series Resonance Z = R
and I = V/Z=V/R = 10/10
= 1 A

S8. Ans.(b)
Sol. In an RLC series resonant circuit,
Z = minimum and denoted by Z_min=R
i.e., In Case of series Resonance.
(i) X_L=X_C
(ii) Z = minimum & Z = R
(iii) Pf = unity (i.e., Resistive circuit)

S9. Ans.(b)
Sol. Resistance α 1/Conductance

S10. Ans.(a)
Sol. for series connection I is same.
P α 1/R
So, lower power rating will glow more.

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