Quiz: Electrical Engineering 26 Aug 2020

Quiz: Electrical Engineering
Topic: Miscellaneous

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

Q1. While conducting short circuit test on a transformer the following side is short circuited:
(a)High voltage side
(b)Low voltage side
(c)Primary side
(d)Secondary side

Q2. The main disadvantages of using short pitch winding in alternators is that it…….
(a)Reduces harmonics in the generated voltage
(b)Reduces the total voltage around the armature coils
(c)Produces asymmetry in the three phase windings
(d)Increase Cu of end connections

Q3. Out of the following methods of heating the one which is independent of supply frequency is
(a)Electric arc heating
(b)Induction heating
(c)Electric resistance
(d)Dielectric heating

Q4. An RLC series circuit of R=4Ω inductive reactance =6Ω and capacitive =3Ω is connected across a 220 V, 50 Hz single phase AC supply. Power factor of the circuit is:
(a) 0.6 leading
(b) 0.8 lagging
(c) 0.6 lagging
(d) 0.8 leading

Q5. Potentiometer is basically a device for:
(a) measuring a current
(b) comparing two voltages
(c) comparing two currents
(d) measuring a voltage

Q6. Which of the following generators have two field windings?
(a)Series wound generator
(b)Shunt wound generator
(c)Compound wound generator
(d)All of the above

Q7. The equalizer rings are used in
(a)Lap winding
(b)Wave winding
(c)Multilayer wave winding
(d)None of these

Q8. In an RLC series circuit the condition below the resonant frequency is:
(a)Xc > XL
(b)Xc + XL
(c)Xc < XL
(d)Xc = XL

Q9. What is the main drawback of paper as an insulating material?
(a)Has poor dielectric strength
(b)Has low insulation resistivity
(c)Has high capacitance
(d)It is hygroscopic

Q10. The unit of luminous flux is:

S1. Ans.(b)
Sol. During short-circuit test of a transformer, low voltage side is short-circuited and during open circuit test, high voltage side is open circuited.

S2. Ans.(b)
Sol. if the coil span is less than the pole pitch, then the winding is referred as short pitched. Short-pitches coils reduce the amount of copper needed and it eliminates the harmonics and improves the waveform of generated emf.
The disadvantage of using short-pitch winding is that the total voltage around the coils is somewhat reduced.

S3. Ans.(c)
Sol. Heating by resistance methods is independent of frequency.

S4. Ans.(b)
Sol. When XL>XC: the phase angle Ф is positive and the circuit is inductive. The circuit behaves like a series RL circuit. i.e. lagging power factor.
For given problem: Z=√(R^2+(XL-XC )^2 )
∴Z=√(4^2+(6-3)^2 )=5 Ω
And power factor=R/Z=4/5=0.8 lagging

S5. Ans.(b)
Sol. A potentiometer is an instrument for measuring voltage or ‘potential difference’ by comparison of an unknown voltage with a known reference voltage.

S6. Ans.(c)
Sol. In a Compound Wound Generator, there are two sets of the field winding on each pole. One of them is connected in series having few turns of thick wire, and the other is connected in parallel having many turns of fine wire with the armature windings.

S7. Ans.(a)
Sol. To overcome the detrimental effects resulting from the circulating currents, it is customary to employ equalizer connections in all lap wound armatures.
Therefore, the function of equalizer rings is to avoid unequal current distribution at the brushes and to reduce sparking between brushes and commutator. The equalizer rings are low resistance copper conductor which connects those points in the armature winding which have potential difference between them.

S8. Ans.(a)
Sol. In an RLC series circuit, below the resonant frequency: Xc > XL (capacitive nature)

S9. Ans.(d)
Sol. The only disadvantage is that paper is hygroscopic and even if it is impregnated with suitable compound, it absorbs moisture and thus lowers the insulation resistance of the cable.

S10. Ans.(b)
Sol. The SI unit of luminous flux is the lumen.

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