RRB-JE'22 EE: Daily Practices Quiz 24-NOV-2021

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EE QUIZ: RRB-JE

RRB-JE’22 EE: Daily Practices Quiz 24-NOV-2021

Each question carries 1 mark.
Negative marking: 1/3 mark
Total Questions: 10
Time: 8 min.

Q1. The form factor of a 220 V, 50 Hz AC waveform is………
(a) 1.11
(b) 0.85
(c) 0.95
(d) 1.41

Q2. What is the unit of illumination?
(a) Henry
(b) Lux
(c) Decibel
(d) Coulomb

Q3. Numbers that are written with base 8 are classified as….
(a) Real numbers
(b) Hexadecimal numbers
(c) Octal numbers
(d) Negative numbers

Q4. Which of the following causes permanent damage to a transmission line insulator?
(a) Corona discharge
(b) Puncture
(c) Dry band arcing
(d) Flashover

Q5. A shunt generator running at 1000 RPM has generated EMF of 100 V. If the speed increases to 1200 RPM, then the generated EMF will be………
(a) 120 V
(b) 240 V
(c) 175 V
(d) 140 V

Q6. Relative permeability of a substance is less than the permeability of free space is known as………
(a) Paramagnetic
(b) Non magnetic
(c) Diamagnetic
(d) Ferromagnetic

Q7. The range of efficiency for shaded pole motors is
(a) 95% to 99%
(b) 80% to 90%
(c) 50% to 75%
(d) 5% to 35%

Q8. If the maximum current of a half-wave rectified wave is 10 A, its RMS value is given by
(a) 7.07 A
(b) 5.0 A
(c) 6.37 A
(d) 10 A

Q9. The short circuit test in a transformer is used to determine……
(a) Eddy current
(b) Hysteresis loss
(c) Copper loss at any load
(d) Iron loss at any load

Q10. A SCHOTTKY diode is a:
(a) Minority carrier device
(b) Majority carrier device
(c) Both minority and majority carrier diode
(d) Fast recovery diode

SOLUTIONS

S1. Ans.(a)
Sol. For the current varying sinusoidally, the Form Factor is given as:
Form factor=I_rms/I_av =((I/√2))/(2I_m/π)=1.11

S2. Ans.(b)
Sol. Illumination is the luminous flux received by a surface per unit area. Its unit is Lux or meter-candle or lumens per m^2.

S3. Ans.(c)
Sol. The most commonly and widely used bases are binary number system (Base-2), octal number system (Base-8), decimal number system (Base-10), and hexadecimal number system (base-16).

S4. Ans.(b)
Sol. As puncture destroys the insulator. It is more serious than flash-over.
The greater the safety factor, the lower is the probability that an insulator will be punctured in an event of flashover. Safety factors can be calculated by dividing puncture voltage by the flashover voltage of an insulator.

S5. Ans.(a)
Sol. For DC machines; E α ϕN
For shunt generator: ϕ=constant ⇒ Eg α N
∴Eg2/Eg1 =N2/N1 ⇒Eg2=N2/N1 ×Eg1=1200/1000×100=120 V

S6. Ans.(c)
Sol. Diamagnetic
Relative permeability is less than that of the free space.
Negative susceptibility
NOTE:
Relative permeability=1+Magnetic susceptibility
Since both paramagnetic and ferromagnetic materials have positive susceptibility, their relative permeability is greater than unity i.e., their permeability is more than the permeability of free space.

S7. Ans.(d)
Sol. The range of efficiency for shaded pole motors is 5% to35%.
Shaded pole motors are used where low torque is acceptable (such as fans) and are usually less than ¼ HP. Due to their very low efficiency, shaded pole motors should only be used in applications where the motor is very small or operates for very short period of time (e.g., shower fan motor).

S8. Ans.(b)
Sol. For half-wave rectifier: I_rms=Im/2=10/2=5 A

S9. Ans.(c)
Sol. SC test of transformer:
Used to determine copper loss or ohmic loss
LV side short-circuited
Instruments kept on the HV side
Also determines equivalent resistance and leakage reactance

S10. Ans.(b)
Sol. A SCHOTTKY diode is a majority carrier device and formed by the junction of a semiconductor with a metal.