Quiz: Electrical Engineering 6 Aug 2020

Quiz: Electrical Engineering
Topic: Miscellaneous

Each question carries 1 mark.
Negative marking: 1/3 mark
Time: 10 Minute

Q1. Differentially compound D.C. motors can find applications requiring
(a)high starting torque
(b) variable speed
(c) low starting torque
(d)frequent on-off cycles

Q2. Megger is an instrument by which we can measure
(a) high resistance
(b) low resistance
(c) high current
(d) high voltage

Q3. The purpose of coating on arc welding electrodes is to
(a) stabilize the arc
(b) provide a protecting atmosphere
(c) provide slag to protect the molten metal
(d) all of the above

Q4. Illumination of one lumen per sq. meter is called . . .
(a)lumen meter
(c)foot candle

Q5. A star circuit has element of resistance R/2. The equivalent delta elements will be
(a) R/6
(b) 3/2 R
(c) 2R
(d) 4R

Q6. A 230 V D.C. shunt motor takes 323 A at full load. The back e.m.f. on full load, if the
resistance of motor armature and shunt field windings are 0.02 Ω and 115 Ω respectively, will be
(a) 210 V
(b) 215 V
(c) 220 V
(d) 224 V

Q7. D.C. generator generally preferred for charging automobile batteries is
(a)series generator
(b)shunt generator
(c)long shunt compound generator
(d)any of the above

Q8. The inductance of a high Q inductor can be measured using a
(a) Schering bridge
(b) Wein bridge
(c) Maxwell bridge
(d) Hay’s bridge

Q9. Which of the following motors is preferred for traction work?
(a) Universal motor
(b) D.C. series motor
(c) Synchronous motor
(d) All of the above

Q10. If the no load voltage of a certain generator is 210 V and the rated voltage is 200 V, then the voltage regulation is
(b) 5%
(c) 10 %
(d) 15 %

S1. Ans.(c)
Sol. Differentially compound d.c. motors are used for low starting torque requirements

S2. Ans.(a)
Sol. The two instruments you will use most often to check continuity, or to measure the resistance of a circuit or circuit component, are the OHMMETER and the MEGGER (MEGOHMMETER). The ohmmeter is widely used to measure resistance and to check the continuity of electrical circuits and devices. Its range usually extends to only a few megohms. The megger is widely used for measuring insulation resistance, such as that between a wire and the outer surface of its insulation, and the insulation resistance of cables and insulators. The range of a megger can be extended to more than 1,000 megohms.

S3. Ans.(d)
Sol. The primary purpose of a light coating is to increase arc stability, provide a protective
gaseous atmosphere to prevent oxygen, hydrogen, and nitrogen picks up by the molten
metal and Protective slag over hot metal etc.

S4. Ans.(b)
Sol. The amount of light that is cast on a surface is called illuminance, which is measured
in lux. This can be thought of as light intensity within a specific area.
LUX is an abbreviation for Lumens per square meter.

S5. Ans.(b)
Sol. R/2 → In star connection
∴R_Δ=3*(R/2) → In delta connection

S6. Ans.(d)
Sol. Vt=230V , IL=323 A

Ra=0.02Ω Rsh=115Ω
Ea=V-Ia Ra
=321 A
=223.58≃224 V

S7. Ans.(b)
Sol. Shunt generator are used because they provide constant terminal voltage.

S8. Ans.(d)
Sol. The Hay’s bridge is used for determining the self-inductance of the circuit. The bridge is the advanced form of Maxwell’s bridge. The Maxwell’s bridge is only appropriate for measuring the medium quality factor. Hence, for measuring the high-quality factor the Hays bridge is used in the circuit.

S9. Ans.(b)
Sol. DC motors are used for traction as, according to the characteristics of DC motors
speed is inversely proportional to torque and square of armature current as well, if linear
magnetization is concerned. Thus, DC motors are perfectly suitable for traction.
It has high starting torque which is important in traction system. It requires less power
for high torque production because torque production is directly proportional to the
square of the armature current.

S10. Ans.(b)
V.R.% = (No load voltage-Full load voltage )/(Full load voltage)×100

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