Quiz: Electrical Engineering 08 Oct 2020

Quiz: Electrical Engineering
Topic: Miscellaneous

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

Q1. If the modulation index of an amplitude modulated wave is changed from 0 to 1, then the transmitted power will be
(a) Zero
(b) Doubled
(c) Unchanged
(d) Increase by 50 %

Q2. Three resistances P, Q, R each of 2Ω and an unknown resistance S form the four arms of a Wheatstone bridge circuit. When a resistance of 6Ω is connected in parallel to S the bridge gets balanced. What is the value of S?

(a) 1 Ω
(b) 2 Ω
(c) 3 Ω
(d) 6 Ω

Q3. To avoid cogging in induction motor, the number of stator slots should not be ______________ the number of rotor slots.
(a) greater than
(b) dependent on
(c) equal to
(d) less than

Q4. Which of the following device is commonly used for lightening protection?
(a) isolator
(b) Over voltage relay
(c) Circuit breaker
(d) ZnO Varistor

Q5. A SCHOTTKY diode is a:
(a) Both minority and majority carrier diode
(b) Minority carrier device
(c) Fast recovery diode
(d) Majority carrier device

Q6. Multi-meters cannot be used to measure:
(a) resistance
(b) current
(c) voltage
(d) frequency

Q7. A second-order servo has unity feed and an open-loop transfer function: G(S) = 500/s(s+15). The settling time is:
(a) 2 sec
(b) 0.53 sec
(c) 500 sec
(d)0.5 sec

Q8. A single phase, full-wave, fully controlled bridge converter for supplying high inductive load is fed by a voltage V_m sin⁡ωt. The average and rms value of output voltages are
(a) (2Vm)/π cos⁡α and Vm/√2
(b) Vm/π cos⁡α and Vm/√2
(c) (2Vm)/π cos⁡α and Vm
(d) Vm/π cos⁡α and √2 Vm

Q9. Which testing method is performed to determine No Load losses in DC motor?
(a) Running down test
(b) Field test
(c) Swinburne’s test
(d) Brake test

Q10. The pointer returns to its zero position on removing the source producing the deflecting torque. This happens due to:
(a) Controlling torque
(b) Balancing torque
(c) Damping torque
(d) Mass of pointer

S1. Ans.(d)
Sol. the transmitted power in AM wave is: Pt=Pc (1+µ^2/2)
Where, µ= modulation index
Pc= power in carrier wave
When, µ=0, Pt=Pc
When, µ=1, Pt=Pc (1+1/2)=1.5 Pc
∴% increase in transmitted power=(1.5Pc-Pc)/Pc *100%=50%

S2. Ans.(c)
Sol. let X be the equivalent resistance between S and 6 Ω.
∴1/X=1/6 +1/S…………… (1)

For a balanced Wheatstone bridge, we get: P/Q=R/X
⇒2/2=2/X ⇒X=2 Ω
Putting this value in eq. (1), 1/2=1/6+1/S
⇒S=3 Ω

S3. Ans.(c)
Sol. To avoid cogging in induction motor, the number of stator slots should not be equal to the number of rotor slots.

S4. Ans.(d)
Sol. In modern era, gap less ZnO or zinc oxide surge arresters are mainly used for surge protection.

S5. Ans.(d)
Sol. Schottky diode is formed by joining a semiconductor region (usually N-type) with a metal such as gold, silver or platinum. So, it is a metal to semiconductor junction having only the majority carriers.

S6. Ans.(d)
Sol. A typical multi-meter can measure voltage, current, and resistance.

S7. Ans.(b)
Sol. characteristics eq.: 1+ G(s)H(s)=0
From above eq. 2ξωn=15
Settling time=4/ ξωn=8/15=0.53 s

S8. Ans.(a)
Sol. A single phase, full-wave, fully controlled bridge converter for supplying high inductive load: Vavg=(2Vm)/π cos⁡α
And Vrms=Vm/√2

S9. Ans.(c)
Sol. Swinburne’s test is the most commonly used and simplest method of testing of shunt and compound wound DC machines which have constant flux.
In this method of testing no load losses are measured separately and eventually we can determine the efficiency.

S10. Ans.(a)
Sol. Controlling torque brings the pointer back to zero when the deflecting torque is removed. If it were not provided, the pointer once deflected would not return to zero position on removing the deflecting torque.


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