Quiz: Electrical Engineering 28 Nov 2020

Quiz: Electrical Engineering
Exam: RSMSSB-JEn
Topic: Miscellaneous

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

Q1. Which of the following statement is false?
(a) Transformer is a constant flux machine
(b) Silica gel is used in transformers
(c) Induction motor can be self-starting
(d) Synchronous motor is self-starting

Q2. The size of a synchronous motor decreases with the increase in
(a) Horse power rating
(b) Speed
(c) Flux density
(d) All of the above

Q3. The E_b/V ratio of a DC motor is an indication of its
(a) Speed regulation
(b) Efficiency
(c) Running torque
(d) Starting torque

Q4. The yoke of small DC machine is made up of
(a) Cast iron
(b) Copper
(c) Stainless steel
(d) Aluminium

Q5. The voltage coil of a single-phase house service energy meter
(a) Is highly resistive
(b) Is highly inductive
(c) Is highly capacitive
(d) Has a phase angle equal to load power factor angle

Q6. What quantity of charge must be delivered by a battery with a Potential Difference of 110 V to do 660J of Work?
(a) 0.6 C
(b) 6 C
(c) 60 C
(d) 600 C

Q7. An induction motor has a rotor resistance of 0.002Ω/phase. If the resistance increased to 0.004Ω/phase then the maximum torque will
(a) Reduced to half
(b) increased by 100%
(c) Increased by 200%
(d) Remain unaltered

Q8. Ferranti effect can be compensated by which of the following
(a) Shunt capacitor
(b) Shunt reactor
(c) Series capacitor
(d) Both a and b

Q9. Furnaces used for cremation use
(a) Dielectric heating
(b) Arc heating
(c) Resistance heating
(d) Induction heating

Q10. In an electric heater, the metal case is connected to…………
(a) Phase wire
(b) earth wire
(c) neutral wire
(d) none of these

SOLUTIONS
S1. Ans.(d)
Sol. synchronous motor is not self-starting.

S2. Ans.(c)
Sol. A α 1/Bm
So, The size of a synchronous motor decreases with the increase in flux density.

S3. Ans.(b)
Sol. Electrical motor efficiency is defined that the ratio of mechanical power developed to the total electrical power input.
So, efficiency = EbIa/VIL.
Hence, the Eb/V ratio of a DC motor is an indication of its efficiency.

S4. Ans.(a)
Sol. The yoke of small DC machine is made up of cast iron.

S5. Ans.(b)
Sol. The voltage coil of a single-phase house service energy meter is highly inductive.

S6. Ans.(b)
Sol. Q = W / V = 660J / 110V = 6C

S7. Ans.(d)
Sol. Maximum torque in an induction motor, T_MAX ∝1/2X.
the maximum torque is independent of rotor resistance and is inversely proportional to rotor reactance. So, if we increase the rotor resistance the maximum torque will be unaltered.

S8. Ans.(b)
Sol. Ferranti effect occurs in case of no load or light load condition of a medium and long transmission lines due to capacitance effect of the transmission line.
Shunt reactor will reduce the effect of capacitance. Therefore, Ferranti effect will be reduced.

S9. Ans.(c)
Sol. furnaces used for cremation purpose uses Resistance heating.

S10. Ans.(b)
Sol. In an electric heater, the metal case is connected to ‘earth wire’ for protection against fault.

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