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MCQ
41. Which of the following lamp has minimum initial cost of installation but maximum running cost?
incandescent
fluorescent
mercury vapour
sodium vapour
ব্যাখ্যা: Incandescent lamp has higher resistance compare to other lamps. As a result more electricity is used to run this blubs. So the running cost is high.
42. At parallel resonance-
circuit impedance is minimum
power factor is zero
line current is maximum
power factor is unity
43. What is the peak-to-peak value for 120V ac?
240V
339V
480V
391V
44. Which of the following connections is best suited for 3-phase, 4-wire service?
Δ-Δ
Y-Y
Δ-Υ
Y-A
ব্যাখ্যা: Δ-Υ connection is popular for both the step (transmission side, high voltage) and step-down (distribution zide, low voltage) applications
45. যদি Delta সার্কিটে একটি phase open করা হয় তাহলে Total power এর কত অংশ কমবে?
1/3 অংশ
1/2 অংশ
2 অংশ
কোনোটিই নয়
46. Inductance opposes --in current in a circuit
only increase
change
only decrease
none of the above
ব্যাখ্যা : According to Lenz's law, the induced voltage has a polarity (direction) which opposes the change in current that created it. As a result, inductors oppose any changes in current.
47. For Y-connection under balanced condition the line to line voltage is-
same as the phase voltage
√3 times the phase voltage
√2 times the phase voltage
none of the above
48. The unit of inductance—
Inducta
henry
inductive reactance
ohm
49. Inductance opposes --in current in a circuit.
only increase
change
only decrease
none of the above
ব্যাখ্যা : According to Lenz's law, the induced voltage has a polarity (direction) which opposes the change in current that created it. As a result, inductors oppose any changes in current.
50. If a phase is multiplied by j, then –
only its magnitude changes
only its direction changes
both magnitude & direction changes.
none of above
ব্যাখ্যা: It we multiplied by then the phase direction will rotate through a fixed angle of 90° in an anticlockwise direction. In each successive rotation, the magnitude of the vector always remains the same.
51. The average value of a sinusoidal current is 100A. Its rms value is-
70.7A
63.7A
141.4A
111A
52. The phase sequence of a three-phase system is RYB. The other possible phase sequence can be-
BRY
YRB
RBY
none of the above
53. What is the power frequency (Hz) of Bangladesh?
30
60
50
None
54. Four capacitors each of 40µF are connected in parallel, the equivalent capacitance will be-
160µF
40µF
10µF
5µF
55. At parallel resonance the circuit impedance equals to-
L/CR
LC/R
RL/C
CR/L
56. In a series R.L circuit, voltage across resistor inductor are 3V and 4V respectively, then what is the applied voltage?
7V
4V
5V
3V
57. The capacitive reactance of a circuit is-frequency.
independent of
inversely proportional to
directly proportional to
none of the above
58. একটি Heater 230/250 voltage-এ উত্তপ্ত হয়। যখন 250 volt সরবরাহ পায় তখন 5 Amp বিদ্যুৎ প্রবাহিত হয়, তবে যখন 230 volt সরবরাহ পায় তখন কত বিদ্যুৎ প্রবাহিত হবে?
3.6
5.6
4.6
কোনোটিই নয়
59. Two identical capacitors are connected in parallel and charged to a potential of V. They are separated and then connected in series. The potential across the series combination is-
V
3V
4V
2V
60. RMS value of the instantaneous ac voltage V = 300 is-
300x√2
300/√2
300x√3
300/√3