EC
Engineering Classroom
by Himalay Sen

Exams

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Board Questions

Access past board exam questions organized by year and subject to help you understand patterns, improve preparation, and boost your exam performance.

MCQ
4661. The power factor of an ordinary electric bulb is--
Zero
Unity
Slightly more than zero
Slightly less than unity
ব্যাখ্যা: ব্যাখ্যা: Basically ordinary electric bulb are resistive load. As resistive load they have unity power factor.
4664. How long does it take 50 µC of charge to pass a point in a circuit if the current flow is 15 mA?
3.33 x 10^3s
6 x 10^3s
6.33 × 10^3s
2s
4666. 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: 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.
4668. 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
4669. An air-core choke coil and an electric bulb are connected in series with ac mains. On introducing soft iron bar in the coil, the intensity of light will-
fluctuate
remain unchanged
increase
decrease
4671. 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
4674. Which of the following lamp has minimum initial cost of installation but maximum running cost?
incandescent
fluorescent
mercury vapour
sodium vapour
ব্যাখ্যা: 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.
4678. 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
4679. 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
4680. Which of the following connections is best suited for 3-phase, 4-wire service?
Δ-Δ
Y-Y
Δ-Υ
Y-A
ব্যাখ্যা: ব্যাখ্যা: Δ-Υ connection is popular for both the step (transmission side, high voltage) and step-down (distribution zide, low voltage) applications