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MCQ
6441. Four capacitors each of 40µF are connected in parallel, the equivalent capacitance will be-
160µF
40µF
10µF
5µF
6442. 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
6443. What is the peak-to-peak value for 120V ac?
240V
339V
480V
391V
6444. 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.
6445. At parallel resonance-
circuit impedance is minimum
power factor is zero
line current is maximum
power factor is unity
6446. At parallel resonance the circuit impedance equals to-
L/CR
LC/R
RL/C
CR/L
6447. 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.
6448. The d.c. series motor should never be switched on at no load because-
the field current is zero
the machine does not pickup
the speed becomes dangerously high
it will take too long to accelerate
ব্যাখ্যা: No mechanical load on the series motor, the current is low, the counter-EMF produced by field winding is weak and so the armature most turn faster to produce sufficient counter EMF to balance the supply voltage. The motor can be damage by overspeed.
6449. The power factor of an ordinary electric bulb is--
Zero
Unity
Slightly more than zero
Slightly less than unity
ব্যাখ্যা: Basically ordinary electric bulb are resistive load. As resistive load they have unity power factor.
6450. The unit of inductance—
Inducta
henry
inductive reactance
ohm
6451. The average value of a sinusoidal current is 100A. Its rms value is-
70.7A
63.7A
141.4A
111A
6452. 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.
6453. The phase sequence of a three-phase system is RYB. The other possible phase sequence can be-
BRY
YRB
RBY
none of the above
6454. 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
6455. RMS value of the instantaneous ac voltage V = 300 is-
300x√2
300/√2
300x√3
300/√3
6456. One Horse Power is equal to-
5.50 Foot pound/Second
55.00 Foot pound/Second
550 Foot pound/Second
5500 Foot pound/Second
6457. For an R-L load ---
Active power is greater than apparent power
Reactive power is greater than apparent power
Apparent power is greater than both Active and Reactive power
All are equal
6458. 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.
6459. 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
6460. The capacitive reactance of a circuit is-frequency.
independent of
inversely proportional to
directly proportional to
none of the above