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RVUNL’21 EE: Daily Practices Quiz 07-Sep-2021

RVUNL Recruitment 2021: The RVUNL exam date is released for a total of 1075 vacancies.
There are two parts for the RVUNL test, Part A and Part B.
Part A will have 60% weightage while Part B has 40% weightage out of the total marks in the online written exam.

RVUNL’21 EE: Daily Practices Quiz 07-Sep-2021
Each question carries 2 marks.
Negative marking: 0.5 mark
Total Questions: 06
Time: 08 min.

Q1. Expansion during heating results in which of the following?
(a) Increases the weight of the material
(b) Occurs only in solid
(c) Decreases the density of the material
(d) Occurs at the same rate of all liquids and solids
(e) All of the above

Q2. The electrical conductivity of an intrinsic semiconductor at 0K is
(a) less than that of an insulator
(b) is equal to zero
(c) is equal to infinity
(d) more than that of an insulator
(e) is equal to that of a metal

Q3. Which gas is inside an electric bulb?
(a) Air
(b) Oxygen
(c) Carbon dioxide
(d) All of the above
(e) None of the above

Q4. What gases are filled in fluorescent tube?
(a) Neon
(b) Mercury
(c) Sodium
(d) Mercury, Neon, Argon
(e) None of the above

Q5. A 6-pole, 3-phase alternator running at 1000 rpm supplies to an 8-pole, 3-phase induction motor which has a rotor current of frequency 2 Hz. The speed at which the motor operates is
(a) 750 rpm
(b) 720 rpm
(c) 960 rpm
(d) 1000 rpm
(e) 705 rpm

Q6. The results of a ‘slip test’ for determining direct-axis(X_d) and quadrature-axis(X_q) reactance of a star-connected, salient pole alternator is given below:
Phase values: V_max=100 V;〖 V〗_min=96 V; I_max=12 A;〖 I〗_min=10 A.
Hence the two reactances will be:
(a) X_d=8.33 Ω and X_q=9.6 Ω
(b) X_d=9.6 Ω and X_q=8.33 Ω
(c) X_d=10 Ω and X_q=8 Ω
(d) X_d=8 Ω and X_q=10 Ω
(e) X_d=8.25 Ω and X_q=9.6 Ω

SOLUTIONS

S1. Ans.(c)
Sol. As we know. Density=mass/volume.
During expansion, mass of the matter remains constant but its volume increases and hence density decreases.
Expansion occurs in all the states of matter and having different rate of expansion.

S2. Ans.(b)
Sol. The conductivity of an intrinsic semiconductor decreases with decrease in temperature and so it behaves as an insulator at 0K. The conductivity of an insulator is zero. Therefore. the electrical conductivity of an intrinsic semiconductor at 0K is equal to zero.

S3. Ans.(e)
Sol. The bulb consists of filament positioned inside a glass bulb surrounded by inert gas (combination of argon and inactive nitrogen).

S4. Ans.(d)
Sol. A fluorescent tube is filled with a gas containing low-pressure mercury vapour and argon, neon, xenon or krypton. The pressure is around 0.3 % of atmospheric pressure.

S5. Ans.(b)
Sol. Supply frequency(f)=(1000×6)/120=50 Hz
Slip frequency: sf=2 (ACQ)
∴slip(s)=2/50=0.04
∴N_s=120f/P=(120×50)/8=750 rpm
∴N_r=N_s (1-s)=750×(1-0.04)=720 rpm

S6. Ans.(c)
Sol. From slip test: X_d=V_max/I_min =100/10=10 Ω
And X_q=V_min/I_max =96/12=8 Ω

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