Question 1 |
In a series RLC circuit at resonance, the magnitude of the voltage developed
across the capacitor
is always zero | |
can never be greater than the input voltage | |
can be greater than the input voltage, however, it is 90^{\circ} out of phase with
the input voltage | |
can be greater than the input voltage, and is in phase with the input voltage. |
Question 1 Explanation:
In a series RLC circuit, at resonance
V_L=jQV_{source} and V_c=-jQV_{source}
also for Q \gt 1, |V_c| \gt |V_{source}|
Hence, option (C) is correct.
V_L=jQV_{source} and V_c=-jQV_{source}
also for Q \gt 1, |V_c| \gt |V_{source}|
Hence, option (C) is correct.
Question 2 |
Two incandescent light bulbs of 40 W and 60 W rating are connected in series
across the mains. Then
the bulbs together consume 100 W | |
the bulbs together consume 50W | |
the 60 W bulb glows brighter | |
the 40 W bulb glows brighter |
Question 2 Explanation:
\because \;\;P\propto \frac{1}{R}
Therefore , resistance of 40 W bulb \gt resistance of 60 W bulb.
For series connection, current through both the bulbs will be same P=I^2R (for series connection).
Power consumed by 40 W bulb \gtPower consumed by 60 W bulb.
Hencem the 40 W bulb glows brighter.
Therefore , resistance of 40 W bulb \gt resistance of 60 W bulb.
For series connection, current through both the bulbs will be same P=I^2R (for series connection).
Power consumed by 40 W bulb \gtPower consumed by 60 W bulb.
Hencem the 40 W bulb glows brighter.
Question 3 |
A unit step voltage is applied at t = 0 to a series RL circuit with zero initial
conditions.
It is possible for the current to be oscillatory. | |
The voltage across the resistor at t = 0^{+} is zero. | |
The energy stored in the inductor in the steady state is zero. | |
The resistor current eventually falls to zero. |
Question 3 Explanation:
At t=0^+ inductor works as open circuit. Hence, complete source voltage drops across it and consequently, current through the resistor R is zero. Hence, voltage across the resistor at t=0^+ is zero. And further with time it rises accroding to V_R(t)=(1-e^{-Rt/L})u(t).


Question 4 |
Given two coupled inductors L_{1} and L_{2}, their mutual inductance M satisfies
M=\sqrt{L^{2}_{1}+L^{2}_{2}} | |
M \gt \frac{\left ( L_{1}+L_{2} \right )}{2} | |
M\gt \sqrt{L_{1}L_{2}} | |
M\leq \sqrt{L_{1}L_{2}} |
Question 4 Explanation:
M=K\sqrt{L_1L_2}
where , K= coefficient of coupling
\because \; 0 \lt K \lt 1
\therefore \; M \leq \sqrt{L_1L_2}
where , K= coefficient of coupling
\because \; 0 \lt K \lt 1
\therefore \; M \leq \sqrt{L_1L_2}
Question 5 |
A passive 2-port network is in a steady-state. Compared to its input, the steady
state output can never offer
higher voltage | |
lower impedance | |
greater power | |
better regulation |
Question 5 Explanation:
For a passive two port network, output powe can never be grater than input power.
Question 6 |
A single-phase transformer is to be switched to the supply to have minimum
inrush current. The switch should be closed at
maximum supply voltage | |
zero supply voltage | |
\frac{1}{\sqrt{2}} maximum supply voltage | |
1/2 maximum supply voltage |
Question 6 Explanation:
When the value of input voltage is maximum, rate of change of core flux is minimum, as both are 90^{\circ} out of phase in case of sinusoidal input.
Question 7 |
It is desirable to eliminate 5th harmonic voltage from the phase voltage of an
alternator. The coils should be short-pitched by an electrical angle of
30^{\circ} | |
36^{\circ} | |
72^{\circ} | |
18^{\circ}
|
Question 7 Explanation:
For fifth harmonics, 5\beta =180^{\circ}
\Rightarrow \;\;\beta =36^{\circ}
\Rightarrow \;\;\beta =36^{\circ}
Question 8 |
Figure shows the magnetization curves of an alternator at rated armature
current, unity power factor and also at no load. The magnetization curve for rated
armature current, 0.8 power factor leading is given by


curve A | |
curve B | |
curve C | |
curve D |
Question 9 |
The core flux of a practical transformer with a resistive load
is strictly constant with load changes | |
increases linearly with load | |
increases as the square root of the load | |
decreases with increased load |
Question 10 |
X_{d} , {X}'_{d} and {X}''_{d}
are steady state d-axis synchronous reactance, transient d-axis
reactance and sub-transient d-axis reactance of a synchronous machine
respectively. Which of the following statements is true?
X_{d} \gt {X}'_{d} \gt {X}"_{d} | |
{X}''_{d} \gt {X}'_{d} \gt X_{d} | |
{X}'_{d} \gt {X}''_{d} \gt X_{d} | |
X_{d} \gt {X}''_{d} \gt {X}'_{d} |
There are 10 questions to complete.