Question 1 |

A current impulse 5\delta \left ( t \right ), is forced through a capacitor C. The voltage V_{c}\left ( t \right ),
across the capacitor is given by

5t | |

5u(t) - C | |

\frac{5}{C}t | |

\frac{5u(t)}{C} |

Question 1 Explanation:

V_c(t)=\frac{1}{C}\int_{-\infty }^{t}i(t)dt=\frac{1}{C}\int_{-\infty }^{t}5\delta (t)dt=\frac{5}{C}u(t)

Question 2 |

Fourier Series for the waveform, f(t) shown in figure is

\frac{8}{\pi ^{2}}\left [ \sin \left ( \pi t \right )+\frac{1}{9}\sin \left ( 3\pi t \right )+\frac{1}{25}\sin \left ( 5\pi t \right )+.... \right ] | |

\frac{8}{\pi ^{2}}\left [ \sin \left ( \pi t \right )-\frac{1}{9}\cos \left ( 3\pi t \right )+\frac{1}{25}\sin \left ( 5\pi t \right )+.... \right ] | |

\frac{8}{\pi ^{2}}\left [ \cos \left ( \pi t \right )+\frac{1}{9}\cos \left ( 3\pi t \right )+\frac{1}{25}\cos \left ( 5\pi t \right )+.... \right ] | |

\frac{8}{\pi ^{2}}\left [ \cos \left ( \pi t \right )-\frac{1}{9}\sin \left ( 3\pi t \right )+\frac{1}{25}\sin \left ( 5\pi t \right )+.... \right ] |

Question 2 Explanation:

\because f(t) is an even function with half waves symmetry,

\therefore dc term as well as sine terms=0

Only the cosine terms with odd harmonics will be present.

\therefore dc term as well as sine terms=0

Only the cosine terms with odd harmonics will be present.

Question 3 |

The graph of an electrical network has N nodes and B branches. The number of
links, L, with respect to the choice of a tree, is given by

B - N + 1 | |

B + N | |

N - B + 1 | |

N - 2B -1 |

Question 3 Explanation:

Number of links =B-(N-1) =B-N+1

Question 4 |

Two in-phase, 50 Hz sinusoidal waveform of unit amplitude are fed into channel 1
and channel 2 respectively of an oscilloscope. Assuming that the voltage scale,
time scale and other settings are exactly the same for both the channels, what
would be observed if the oscilloscope is operated in X-Y mode?

A circle of unit radius | |

An ellipse | |

A parabola | |

A straight line inclined at 45^{\circ} with respect to the x-axis |

Question 4 Explanation:

\therefore \;\; \text{Phase difference}=0^{\circ} \text{also} f_x=f_y.

Question 5 |

Given a vector field \vec{F}, the divergence theorem states that

\int _S\vec{F}\cdot d\vec{S}=\int _V\vec{\triangledown }\cdot \vec{F}dV | |

\int _S\vec{F}\cdot d\vec{S}=\int _V\vec{\triangledown }\times \vec{F}dV | |

\int _S\vec{F}\times d\vec{S}=\int _V\vec{\triangledown }\cdot \vec{F}dV | |

\int _S\vec{F}\times d\vec{S}=\int _V\vec{\triangledown }\times \vec{F}dV |

Question 6 |

If a 400V, 50 Hz, star connected, 3 phase squirrel cage induction motor is
operated from a 400 V, 75 Hz supply, the torque that the motor can now provide
while drawing rated current from the supply?

reduces | |

increases | |

remains the same | |

increase or reduces depending upon the rotor resistance |

Question 6 Explanation:

T=3 I^2\frac{R_2}{s}\frac{60}{2 \pi N_s}

As the motor is drawing rated current from the supply.

\begin{aligned} T &=\propto \frac{1}{N_s} \\ T & \propto \frac{1}{\text{frequency}} \;\;\left [ \because \; N_s=\frac{120f}{P} \right ] \end{aligned}

Hence as frequency increases, torque decreases.

As the motor is drawing rated current from the supply.

\begin{aligned} T &=\propto \frac{1}{N_s} \\ T & \propto \frac{1}{\text{frequency}} \;\;\left [ \because \; N_s=\frac{120f}{P} \right ] \end{aligned}

Hence as frequency increases, torque decreases.

Question 7 |

A dc series motor fed from rated supply voltage is overloaded and its magnetic
circuit is saturated. The torque-speed characteristic of this motor will be
approximately represented by which curve of below figure?

Curve A | |

Curve B | |

Curve C | |

Curve D |

Question 7 Explanation:

At saturation , linear characteristic are observed.

Question 8 |

A 1 kVA, 230V/100V, single phase, 50 Hz transformer having negligible winding
resistance and leakage inductance is operating under saturation, while 250 V, 50
Hz sinusoidal supply is connected to the high voltage winding. A resistive load is
connected to the low voltage winding which draws rated current. Which one of
the following quantities will not be sinusoidal?

Voltage induced across the low voltage winding | |

Core flux | |

Load current | |

Current drawn from the source |

Question 9 |

A 400V/200V/200V, 50 Hz three winding transformer is connected as shown in
figure. The reading of the voltmeter, V, will be

0V | |

400V | |

600V | |

800V |

Question 9 Explanation:

The two 200 turns winding are connected in additive polarity. Hence the output voltage will be 400V. The difference of this 400 V and the voltage induced in first winding (i.e. 400 turn) is same.

Question 10 |

The frequency of the clock signal applied to the rising edge triggered D flip-flop shown in figure is 10 kHz. The frequency of the signal available at Q is

10 kHz | |

2.5 kHz | |

20 kHz | |

5 kHz |

Question 10 Explanation:

In toggle mode

f_{out}=\frac{f_{in}}{2}=\frac{10kHz}{2}=5kHz

f_{out}=\frac{f_{in}}{2}=\frac{10kHz}{2}=5kHz

There are 10 questions to complete.