Quiz: Electrical Engineering 28 Dec 2020

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

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

Q1. A 440 V ,3-phase, 10 pole and 50 Hz synchronous motor delivering a torque of 50/π Nm, delivers a power of
(a)500 W
(b)1000 W
(c)50 W
(d)2000 W

Q2. As compared to a split phase motor, a capacitor start motor has………
(a)Higher running torque
(b)Lower starting torque
(c)Higher starting torque
(d)None of the above

Q3. Which of the following voltmeter has least power consumption?
(a)Electrostatic
(b)Moving iron
(c)Induction type
(d)Hot wire

Q4. What will be the transformation ratio of a 550/110 V, 50 Hz single-phase step-down transformer?
(a)5
(b)11
(c)1.1
(d)0.2

Q5. Diffusion capacitance of a PN junction diode………. with forward bias.
(a)Increases
(b)Decreases
(c)Remains the same
(d)May increase or decrease

Q6. The purpose of guard ring in transmission lines is to…………
(a)Reduce the reactance of the line
(b)Increase the earth capacitance of the lowest unit
(c)Reduce the transmission line losses
(d)Reduce the earth capacitance of the lowest unit

Q7. An RLC series resonance circuit boosts:
(a)Inductance
(b)Frequency
(c)Current
(d)Resistance

Q8. The metal surfaces for electrical resistance welding must be
(a)Rough
(b)Clean
(c)Moistened
(d)Coloured

Q9. The most modern method for food processing is
(a)Induction heating
(b)Dielectric heating
(c)Resistance heating
(d)Eddy current heating

Q10. How many earth pits are there for one transformer in a sub-station?
(a)One
(b)Two
(c)Three
(d)Four

SOLUTIONS
S1. Ans.(b)
Sol. Synchronous speed(N_s )=120f/P=(120×50)/10=600 rpm
∴ω=(2πN_s)/60=(2π×600)/60=20π rad/s
power=Tω=50/π×20π=1000 W

S2. Ans.(c)
Sol. Decreasing order of starting torque:
Capacitor start capacitor run > capacitor start > split phase

S3. Ans.(a)
Sol. Electrostatic type has very low power consumption while induction type has very high-power consumption.

S4. Ans.(d)
Sol. Turn ratio=N_1/N_2 =V_1/V_2
Transformation ratio=N_2/N_1 =V_2/V_1 =110/550=0.2

S5. Ans.(a)
Sol. Diffusion capacitance is directly function of applied voltage or current. when forward bias voltage is applied across PN diode, a large number of charges is accumulated near the depletion layer, as a result, large diffusion capacitance occurs,

S6. Ans.(d)
Sol. The purpose of guard ring in transmission lines is to:
Reduce the earth capacitance of the lowest unit
Equal voltage distribution across each disc

S7. Ans.(c)
Sol. RLC series resonance circuit:
X_L=X_C and Z=R
As impedance is lower, the current will be maximum.

S8. Ans.(b)
Sol. Resistance welding is the process of joining metal parts with the application of pressure.
The metal surface should be properly cleaned so that they are free from rust, dust, oil and grease.

S9. Ans.(b)
Sol. Dielectric heating

S10. Ans.(d)
Sol. There are minimum four earth pits will be required for any transformer.
2 for its neutral earthing and 2 connections for its body earthing.

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