Quiz: Electrical Engineering 17 Dec 2020

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

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

Q1. If residual magnetism is NOT present in DC generator, the induced emf at zero speed will be
(a) 10 % of rated voltage
(b) 50% of rated voltage
(c) Same as rated voltage
(d) Zero

Q2. The sparking at the brushes of a dc generator is due to
(a) Reactance voltage
(b) Armature reaction
(c) Light load
(d) High resistance of the brushes

Q3. The maximum demand of a consumer is 2kw and the corresponding daily energy consumption is 30 units. What is the corresponding load factor?
(a) 75%
(b) 62.5%
(c) 50%
(d) 25%

Q4. Sheaths are used in cables to
(a) Provide mechanical strength
(b) Provide proper insulation
(c) Prevent ingress of moisture
(d) None of the above

Q5. In a fluxmeter, the controlling torque is
(a) Produced by spring
(b) Provided by cross coil mechanism
(c) Not provided at all
(d) Produced by weight attached to the moving coil

Q6. In a series resonant circuit, the voltage across the circuit is the same as the voltage across
(a) Inductance
(b) Capacitance
(c) Resistance
(d) None of the above

Q7. In the dynamometer type of wattmeter, which of the coil is split up into two parts?
(a) Pressure coil
(b) Current Coil
(c) Both the pressure coil and current coil
(d) None of these

Q8. Which one of the following methods gives voltage regulation higher than the actual value in an alternator?
(a) ZPF method
(b) MMF method
(c) emf method
(d) ASA method

Q9. Three inductors each of 60 mH are connected in delta. The value of inductance of each arm of the equivalent star connection is
(a) 10 mH
(b) 15 mH
(c) 20 mH
(d) 30 mH

Q10. 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

SOLUTIONS
S1. Ans.(d)
Sol. Residual Magnetism is needed for instant voltage build up. If there is no residual magnetism, then we may connect machine with a battery for just 5-7 seconds to develop some magnetism.
If residual magnetism is NOT present in DC generator, the induced emf at zero speed will be zero.

S2. Ans.(a)
Sol. The sparking at the brushes of a dc generator is due to reactance voltage.

S3. Ans.(b)
Sol. load factor=(avg.load)/(max.demand)=30/(2×24)×100=62.5 %

S4. Ans.(c)
Sol. Inner sheath is used for protecting the cable from moistures which would affect the insulation.
Over-sheath gives the mechanical strength to the cables. It protects the cable from overall damage like moisture, corrosion, dirt, dust, etc.

S5. Ans.(c)
Sol. Flux meter is a special type of ballistic galvanometer provided with a heavy electromagnetic damping and very small controlling torque.

S6. Ans.(c)
Sol. In the RLC series circuit, when the circuit current is in phase with the applied voltage, the circuit is said to be in Series Resonance. The resonance condition arises in the series RLC circuit when the inductive reactance is equal to the capacitive reactance.
i.e., X_L=X_C and Z=R

S7. Ans.(b)
Sol. Fixed Coils or current coil: The dynamometer-type wattmeter essentially consists of two coils called the fixed coil and moving coil. The fixed coil is split into two equal parts that are placed parallel to each other, as shown in Figure. The two fixed coils are air-cored to avoid hysteresis effects when used on AC. The fixed coil is connected in series with the load and carries the circuit current. It is, therefore, called the current coil.

S8. Ans.(c)
Sol. EMF method of voltage Regulation is known as “Pessimistic Method” because gives VR higher than actual.

S9. Ans.(c)
Sol. For equivalent star connection
ZY = (1/3) ZΔ
= 60/3
= 20 mH

S10. 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.

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