BLBCTIlUCAL BNGINBBIlUNG


Candiilotes slwuJd attempt questions 1 and 5 which arecompulsory andanythree oftheremaining questions selection oJ least one question selecting at leastone question/rom e(f£h Section.
SECTION A
Attempt any THREE of the following
For the circuit given be1ow,
Find the frequency w0 at which the impedance across Y reaches a maximum.
(ii)Find the impedance across Y at frequency w0 and the current through the network at that condition. <img src='./qimages/1152-1a2.jpg'>


the difference function given by
y(K 3x(K
If the initial conditions are

and
and the input function is

(ii)Enumerate different properties of the ROC for Laplace transform and find out the I.L.T of s+2 for the different ROC's

A full-pitched coil having N turns rotates with an angular velocity of wr rad/sec with respect of field flux. Obtain an expressiOn for the flux Linkages with the coil as a function of time t Derive there from an expression for the emf generated in the coil Discuss about the two components of the emf expression so obtained.

Show that, in case the field flux is time-invariant, the generated emf lags by 90° the flux that generates it.
you detect a DSBSC signal using an envelope detector? By a suitable analysis, compare the same with coherent detection
A modulating Signal, is given by cos 100t+ 2cos300t. Determine the LSB and USB relations LSB and pie USB If the carrier frequency is 1000 rad
following two amplifier circuit is a generalized immitance converter <img src='./qimages/1152-2a1.jpg'> Analyze the above circuit to get an expression for Zm Assume the two op-amps to be ideal.
With Z1= R1, Z3 R3, Z2 l/C2s, Z4= R4 and Z5= R5,what does the GIC circuit above realize?
Z1 and Z5 are capacitors, Z2,Z3 and Z4 are resistors. How does the input impedance Zm, behave?
(iv)What are energy and power Signals? Compute the energy and power contents of the following Signals and Indicate whether they are energy or power Signals <img src='./qimages/1152-2a4.jpg'>

(b)(i)Discuss why forward break over in a thyristor occurs at a lower anode-cathode voltage If its gate current is increased
(ii)What are the advantages of IGST over BJT, MOSFET and thyristor?
Discuss why the speed control with constant supply voltage and reduced supply frequency is rarely used in practice in a three-phase induction motor. dc machine has total armature ampere conductors of 4500 and total flux in the machine is 0.14 Wb Calculate the torque developed in the machine
A three-phase full converter feeds a resistive load of 150. For a firing-angle delay of the load takes 6RW. Find the magnitude of per phase input supply voltage to the three-phase kill-converter Derive the relevant expression used if any
rectangular pulse exists between T and t Sketch the pulse obtained by convoluting with itself. The Fourier transform of is a sine function Write down the Fourier transform of the pulse obtained by the above convolution.

(ii)Find the Laplace transform 0f the following function
<img src='./qimages/1152-3a2.jpg'>


(b)Explain the development of electromagnetic torque in a three-phase squirrel-cage Induction motor through the interaction of stator and rotor mmf waves. Hence introduce the concept of load angle.
Show that rotor must rotate in the direction of rotating field. Discuss the conditions under which optimum torque is developed in a 3-phase induction motor.

12-V battery feeds a Single-phase full-bridge inverter whose output is connected to an Ideal 1-phase transformer its primary has 10 turns and the load voltage is 230 V For a load resistance of 1OOohm calculate
(i)the number of turns in the transformer secondary winding,

(ii)rms value of primary current, and
(iii)rms value of thyristor current.
Consider only the fundamental component of inverter output voltage.

4.(a)In the circuit shown below the switch'S' closes at t and open after 10 ms. What will be the currents in R,and L1 and L2 and voltage across C1 8ms after switch opens? Assume D,to be an ideal diode and a 0.7 V drop across D2 whenever it conducts.
<img src='./qimages/1152-4a.jpg'>

Show that the field strength at a point close to the antenna (at distances of unto 200-300 miles from the transmitting antenna) in terms of the power is given by
<img src='./qimages/1152-4b.jpg'>
Where:
epsilon is the field strength in volts/m
P is the power radiated in watts
r is the distance in meters

Calculate the field strength at 20 km away from a transmit-ting station of 50 kW power
sine wave carrier is frequency modulated by a triangular modulating Signal as shown in figure below If the carrier frequency iS 100 MHz and modulating Signal frequency is 5 kHz, determine the bandWidth of the FM Signal. Assume frequency deviation constant, Kf 105 Hz/r
<img src='./qimages/1152-4c1.jpg'>

(ii)In a commercial FM broadcast system, the modulation index is the 3dB frequency of the pre-emphasis/de-emphasis filter lS 2100 Hz and message signal frequency is 15 kHz. If the average to peak power ratio of the message Signal is 05, what is the improvement in output SNR of FM with pre-emphasis and de-emphasis filtering compared to a baseband system?


SECTION B
5.Attempt any THREE of the folloWing
What are the criteria for a material to be an imperfect di-electric or a good conductor? Write Maxwell's equations in terms of phasors for Sinusoidally varying electromagnetic fields Consider a uniform plane wave in an isotropic and homogeneous medium, and show that the electric and magnetic field are not in time phase.

uniform plane wave is traveling at a velocity of 3.0 10 m/s in a non-magnetic good conductor and its wavelength lS 0.35 mm Find the frequency of the wave, and the conductivity and the intrinsic impedance of the conductor.

series resonant circuit has its impedance
<img src='./qimages/1152-5b.jpg'>

Find
(i)Resonant frequency
factor
(iii)A and Width
(iv)Impedance under resonance condition.

(c)Two single-phase full converters are used for controlling the speed of a separately-excited dc motor. One full-converter in the field Circuit has zero degree firing-angle delay. Both the converters are connected to 1-phase, 220V, 50 Hz source. DC motor armature resistance is 0.6ohm and field Circuit resistance is 150ohm and its constant is 0.6 V-s/A-rad. Armature and field currents are ripple free.For a firing angle delay of 40° and armature current of 40 determine
(i)The motor speed in rpm,
(ii)Power factor of the armature converter, and
Power factor of the drive scheme.

(d)(i)Define sensitivity, selectivity and fidelity with reference to a radio receiver What is double spotting and its effects on a receiver?

superhet receiver having no RF amplifier, the loaded Q of the antenna coupling circuit is 100. If the superhet is to be improved for HF reception so that its image rejection at 25MHz is as good as at 1100 kHz, determine the loaded Q which an RF amplifier for this receiver would have to have and the new IF that would be needed in the absence of the RF amplifier (Assume IF 0 f 455 kHz)
6.(a)Discuss the criteria for a circuit to oscillate Explain the operation of phase shift oscillator and derive an expression for the frequency of oscillation of an RC phase shift oscillator
A rectangular hollow metal waveguide of internal cross-section 7366cm x 3.556cm carries a 3 GHz Signal in the TE 10 mode. Calculate the maximum power handling capability of the wave guide assuming the maximum permissible electric field inside the waveguide to be 30kV/cm
(ii)Explain how a PLL can be used for demodulation of FM Signals Define capture range and lock range of a PLL.
white Gaussian noise of two sided spectral density 10 -12 V2/Hz is applied to a low pass(RC) filter having a 3 dB cut-off frequency of 1khz find the output noise power.
The received signal is where is the signal and is the noise the signal process is random with an auto correlation <img src='./qimages/1152-6c2.jpg'> the noise is a sample function of a random process with auto correlation e-2|tow|.if the two processes are having zero mean value and are independent of each other determine the autocorrelation and total power of

7.(a)What is uniform plane wave? Define all the parameters associated with it What is meant by group velocity? A uniform plane electro magnetic wave travelling in region 1(epsilonl, mew1,sigma1) is incident normally on a plane boundary separating the region 2(epsilon2,mew2,sigma2), How are the reflected and the transmitted waves at the interface related to the Incident wave?
(b)DistinguiSh AM and NBFM Signals. Obtain an expression for NBFM and WBFM Signals Determine the approXimate band of frequencies occupied by an FM wave With carrier frequency of 5kHz, Kf= 10 Hz/V and 100 cos 200 piet volts.

Distinguish between envelope detection and synchronous detection. Explain a Costas loop receiver for demodulating a DSBSC Signal Explain how the squaring circuit can also be used for synchronous detection
8.(a)(i)Using multiplexers, Implement a full adder circuit.


(ii)It is desired to generate the folloWing three Boolean functions
<img src='./qimages/1152-8a2.jpg'>
By using an OR gate array as shown in Figure, where P1 to P5 are the product terms in one or more of the variables, a,a bar,b,b bar,c and c bar Write down the terms P1, P2, P3,P4 and P5.
50 kW, 440 50Hz, star-connected synchronous generator With Per phase impedance of
0.8 j 4.5ohm, is working With rated terminal voltage. It is required to supply a power of 25 kW to the bus. Estimate the minimum excitation emf Find out the corresponding stator current.

(c)ConSider the Circuit shown below. Main thyristor T1 and auxiliary thyristor TA are off and capacitor is charged to voltage V5 with upper plate positive Sketch the waveforms for i0, ic,iT1,vc,and VTl (assuming constant to ad current), after
(i)thyrstor T1 is turned on
(ii)steady slate is reached in part(i)and then thyristor TA is turned on
<img src='./qimages/1152-8c2.jpg'>
From these waveforms, obtain the expressions for Circuit turn -off time for both SCRs. In case V5 220V, R =10 ohm, and maximum value of current through main SCR is 3 times the load current, calculate the value of commutating inductance L for C 20mewF and the Circuit turn-off time for the auxiliary SCR.