ELECTRICAL AND ELECTRONICS ENGINEERING-SUPPLY 2K3

Code No:RR-12302
I B.Tech. Supplementary Examinations, November-2003
ELECTRICAL AND ELECTRONICS ENGINEERING
(Bio-Technology)
Time:3 hours Max Marks:80
Answer any Five Questions
All questions carry equal marks.
----
1.a) Derive an expression for the total power in a 3-phase circuit in terms of line
voltages and line currents. Show that the power is same whether the load is delta
connected or star connected.
b) A 3-phase balanced star-connected load consists of 100 ohms resistance connected
across a 220V, 3-phase supply. Determine the line currents and total power
consumed.
2.a) Give the constructional features of “CORE” and “Shell” types of transformers, and
give the advantages and disadvantages of each type.
b) A 5 KVA, 2300 / 230V, 50 HZ transformer was tested for the iron loss with normal
excitation and copper losses at full load, and these were found to be 40 watts and 112
watts respectively. Calculate efficiency of the transformer at (i) full load (ii) half full
load. Assume the power factor of the load as 0.8.
3.a) Prove that the concentration of holes in an intrinsic semiconductor is given by
E E KT
v
p N e F V = -( - ) / .
b) Prove that for intrinsic semiconductor 2
i n is proportional to E KT GO T e 3 - / .
4.a) Draw the circuit diagram of half wave rectifier and explain its operation.
b) A half wave rectifier is fed by 220V, 50Hz via a step down transformer of turns ratio
11:1 find (i) the output d.c. and (ii) peak inverse voltage under no load condition.
5.a) Explain qualitatively the three consequences of base-width modulation.
b) Derive relationship between IC and IB for a CE transistor configuration in the active
region.
c) Sketch a family of CE input and output characteristics for the given transistor (npn)
and explain the shape of the curves qualitatively.
6. a) Classify and define the amplifiers depending on the conduction period and sketch the
input and output waveforms.
b) Show that the maximum theoretical efficiency of a class A power amplifier is 50%.
7.a) What kind of feedback is incorporated in the wien bridge oscillator circuit? And why?
b) In a colpitts oscillator using FET, the frequency of oscillations is observed to be
2.5MHz. Oscillator uses L=10mH, C1 = 0.02mF. Find (i) the value of C2 (ii) If L is
doubled the new value of frequency oscillations.
c) Explain about the applications of OPAMP.
8.a) State and prove D Morgau’s theorems.
b) Realize NOR gate using minimum number of NAND gates.
c) Find the 2’S complement of (46)10.
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Set No.
1
Code No:RR-12302
I B.Tech. Supplementary Examinations, November-2003
ELECTRICAL AND ELECTRONICS ENGINEERING
(Bio-Technology)
Time:3 hours Max Marks:80
Answer any Five Questions
All questions carry equal marks.
----
1. With a neat sketch explain the construction and working principle of permanent
magnet moving coil instrument. Derive the torque equation. Explain with suitable
circuits, how PMMC is used as voltmeter?
2.a) Does the induction motor have any similarities with the transformer? Compare
the similarities and differences between them.
b) A 20h.p, 400V, 50HZ, 3-phase induction motor has an efficiency of 80% and working
at 0.7p.f. The motor is connected to 400 volts, 3-phase supply calculate the current
drawn by the motor from the mains.
3.a) Explain the Law of junction for p-n diode.
b) Explain Avalanche and Zener break downs and compare.
c) Derive Diode current equation.
4.a) A full wave bridge rectifier is fed with 220v, 50Hz, through a step-down transformer
of turns ratio 11:1. Assuming ideal diode find the i)d.c. output voltage ii) peak
inverse voltage iii)Rectifier efficiency. The load resistance is 100W.
b) What is ripple factor? Show that the ripple factor for full wave rectifier is 0.482.
5.a) Sketch a family of drain and mutual characteristics and explain the shape of the
curves qualitatively for a JFET.
b) For a source self-bias circuit if ID = 0.8 mA, IDSS = 1.65 mA and VP = -2V find VGS.
6. a) Draw the circuit diagram of push-pull amplifier circuit and explain its operation. List
out the merits of push pull-amplifier.
b) What is meant by crossover distortion – explain.
7. a) Explain the working of Hartley oscillator circuit. Derive the expression for the
frequency.
b) A collector coupled mono stable multi vibrator consists of NPN Si transistors with hFE
of 30, rbb' = 200W, VCC = 10v, VBE = -2v, RC = 5k, RC1 = RC2 = 1k, R=10k, C=0.1mF,
R2=10k, Rb1 = 20k. Calculate the base and collector currents and voltages.
8.a) Explain the working of SR-flipflop.
b) Implement F = A¢B¢C¢ + ABC¢ with NAND gates.
c) Explain Race around conditioning J-K flip flop and how is it eliminated.
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Set No.
2
Code No:RR-12302
I B.Tech. Supplementary Examinations, November-2003
ELECTRICAL AND ELECTRONICS ENGINEERING
(Bio-Technology)
Time:3 hours Max Marks:80
Answer any Five Questions
All questions carry equal marks.
----
1. With a neat sketch explain the construction and working principle of moving iron
(M.I) type instrument. Write down the torque equation.
2.a) Explain the constructional details of a synchronous machine giving the reasons for
making two types of rotors.
b) Explain auxiliary motor starting of synchronous motors.
3.a) Sketch the forward and reverse characteristics of Ge and Si diodes and compare.
b) Design a voltage regulator that will maintain output voltage of 20V across 1.2kW load
with input that varies between 30 and 50V.
c) Derive the expression for Transition capacitance of Diode.
4.a) What are the principle feature of a bridge rectifier. Explain its operation with neat
circuit diagram.
b) Describe the characteristics of a triac.
5.a) Draw a family of drain characteristics and mutual characteristics of an n-channel FET
and explain the shape of the curves qualitatively.
b) Define FET parameters and derive the relationship between them.
6. a) With the help of block diagrams, explain the four different feed back topologies.
b) Draw the circuit of a voltage series feedback amplifier with BJT. What is the effect
of this feedback on Ri and R0.
7.a) Discuss and explain the basic circuit of an LC oscillator and derive the condition for
the oscillations.
b) Compare various multivibrators.
8.a) Explain the principle of 4-bit ripple counter with a diagram.
b) Obtain the truth table of the function F = xy + xy¢ + y¢z
c) Draw the circuit diagram of R-2R ladder D-to-A converter and explain its principle.
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Set No.
3
Code No:RR-12302
I B.Tech. Supplementary Examinations, November-2003
ELECTRICAL AND ELECTRONICS ENGINEERING
(Bio-Technology)
Time:3 hours Max Marks:80
Answer any Five Questions
All questions carry equal marks.
----
1.a) With a neat sketch explain the construction and principle of operation of
dynamometer type watt meter.
b) Two 40w tube lights are ON for a period of six hours a day. Calculate the total energy
consumed by them in a month?
2.a) How e.m.f is induced in the armature of an alternator? What are the factors that
cause a change of the alternator terminal voltage.
b) A 3-phase, 10 pole, star-connected alternator is running at 720 r.p.m. It has a total of
1200 stator conductors the flux per pole 0.056 wb. Determine the induced e.m.f per
phase. Also calculate the line value.
3.a) Explain the formation of depletion layer in an unbiased p-n junction. How does it vary
with (i) bias and (ii) with temperature.
b) Explain about grown and alloy junctions in case of a p-n junction diode.
4.a) Draw the block diagram of a regulated power supply and explain its operation.
b) Determine the value of ripple factor for the output of a Half wave rectifier without
filter.
5.a) Draw the circuit diagram of a fixed bias circuit and derive the expression for stability
factor S. Why this circuit is thermally not stable – Explain.
b) An n-p-n transistor with b = 50 is used in a CE circuit with VCC=10V, RC = 2KW.
The bias is obtained by connecting a 100 KW. resistance from collector to base.
Assume VBE=0V. Find (i) the Quiescent point (ii) the Stability factor S.
6. a) Define class A, B, AB, B and C operation of amplifiers.
b) Draw the circuit diagram of a push-pull amplifier and explain how even harmonics
are eliminated.
c) Derive the relation between gain with feed back and without feedback.
7.a) Explain the operation of monostable multi vibrator with relevant waveforms.
b) How Frequency stability can be improved in the oscillators? Explain.
c) For phase shift oscillator, the feedback network uses R=6kW and C=1500pF. The
transistorized amplifier used, has a collector resistance of 18kW. Calculate the
frequency of oscillations and minimum value of hfe of the transistor.
8.a) Explain the principle of Half-adder. Draw various implementations of sum and carry
of Half-adder.
b) Implement AND and OR gate using discrete components.
c) How do you convert JK-flip-flop to T and D flip-flops.
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Set No.
4