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MCQ
1741. 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.
1742. 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.
1743. Three equal resistor of 100 is connected in series across a source of Emf 30V. What would be the power consumed by each resistor?
10W
90W
30W
60W
1744. What would be the charge of a capacitor 10μF when connected with 20V supply?
200μc
300μc
6200μc
30μc
1745. At parallel resonance the circuit impedance equals to-
L/CR
LC/R
RL/C
CR/L
1746. At parallel resonance-
circuit impedance is minimum
power factor is zero
line current is maximum
power factor is unity
1747. 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
1748. The power of an AC circuit is given by-
VI cosθ
FZ
VI sinθ
FXL
1749. In the maximum value of a current of a circuit is 1 amp (sinusoidal wave). What is the R.M.S. value?
1 Amp
0.637 Amp
0.707 Amp
1.5 Amp
1750. 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.
1751. 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
1752. 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.
1753. The capacitive reactance of a circuit is-frequency.
independent of
inversely proportional to
directly proportional to
none of the above
1754. One Horse Power is equal to-
5.50 Foot pound/Second
55.00 Foot pound/Second
550 Foot pound/Second
5500 Foot pound/Second
1755. RMS value of the instantaneous ac voltage V = 300 is-
300x√2
300/√2
300x√3
300/√3
1756. What is the peak-to-peak value for 120V ac?
240V
339V
480V
391V
1757. 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.
1758. If the power factor of a circuit is unity, its reactive power is-
a maximum
zero
quantity
equal to FR
1759. 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.
1760. 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