12302 Basic Electrical And Electronics Engineering

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Code No: R05012302
Set No. 1
I B.Tech Supplimentary Examinations, Aug/Sep 2008
BASIC ELECTRICAL AND ELECTRONICS ENGINEERING
(Bio-Technology)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks

1. (a) State RMS value of a voltage waveform and nd the RMS value and crest
factor of the waveform v(t) of gure.1a

Figure 1a
(b) What is potential di erence?
(c) An electric heater takes 3 kW at 240 Volts. Calculate the current and resis-
tance of the heating element. [10+2+4]

2. (a) Name the various parts of a D.C machine and give the materials used for each
part. Also show the magnetic path.
(b) Explain the principle of operation of D.C motor. [8+8]

3. (a) For the network shown in the gure 3(a)i determine the range of RL and IL
that will result in VRL being maintained at 10 V.
i. Determine the maximum Wattage rating of the dio de.

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Code No: R05012302
Set No. 1

Figure 3(a)i
ii. The reverse saturation current of the dio de is 1 A. Its peak inverse Volt-
age is 500V. Find ri, Vo that PIV is not exceeded. show in gure 3(a)ii &
gure 3(a)ii

Figure 3(a)ii

Figure 3(a)ii
4. (a) Explain with neat circuit diagram how SCR can be used as HWR.

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Code No: R05012302
Set No. 1
(b) Explain how SCR can be used as a switch.
(c) Explain the turn on mechanism of SCR. [5+5+6]

5. (a) Compare the merits and drawbacks of FET and BJT.
(b) Sketch the basic structure of an n-channel JFET.
(c) De ne the pinch o voltage P and sketch the depletion region before and
after pinch-o and explain the reason. [6+4+6]

6. (a) De ne class A, B, AB, B and C operation of ampli ers.
(b) Draw the circuit diagram of a push-pull ampli er and explain how even har-
monics are eliminated.
(c) Derive the relation between gain with feed back and without feedback.[6+6+4]

7. (a) With the help of neat circuit diagram, explain the following applications of
OP-AMP
i. Multiplier
ii. di erentiator
iii. Subtractor.
(b) Design a scaling adder circuit using OP-AMP, to give the output voltage
o = -(3 1 + 4 2 + 5 3) 1 2 3 are the input voltages given to
the circuit. [10+6]

8. (a) Realize NAND gate using minimum number of NOR gates.
(b) Explain the principle of basic shift registers.
(c) Distinguish between asynchronous and synchronous counters.
(d) Distinguish between Ring and Twisted Ring counters. [4+4+4+4]

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Code No: R05012302
Set No. 2
(Bio-Technology)

1. (a) Determine the voltage VAB in the circuit shown in the gure 1a

Figure 1a
(b) Find the power dissipated in 40 resistor of gure 1b shown. [10+6]

Figure 1b
2. (a) Does the induction motor have any similarities with the transformer. Compare
the similarities and di erences between them.
(b) A 20 h.p, 400 V, 50 Hz, 3-phase induction motor has an e ciency of 80%
and working at 0.7 p.f. The motor is connected to 400 Volts, 3-phase supply
calculate the current drawn by the motor from the mains. [8+8]

3. (a) Draw the energy band diagram of p-n junction under open circuit condition
and explain its operation.

(b) Prove that the dynamic resistance of p-n diode is ˜ n T
I [10+6]

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Code No: R05012302
Set No. 2
4. (a) A HWR has a load of 3.5 kW. If the diode resistance and secondary coil
resistance together have a resistance of 800 and the input voltage has a
signal voltage of peak value 240 V, Calculate
i. Peak, average and RMS value of current owing.
ii. DC power output
iii. AC power input
iv. E ciency of the recti er.
(b) Compare half wave, Center tapped full wave and bridge recti ers. [10+6]

5. (a) Draw the circuit of a transistor (n-p-n) in the CB con guration. Sketch the
input & output characteristics and explain the shape of the curves qualita-
tively.
(b) For the circuit in gure 5b shown for n-p-n transistor, calculate the collector
and base currents. Assume FE = 50. Explain Q point. [8+8]

Figure 5b
6. (a) De ne class A, B, AB, B and C operation of ampli ers.
(b) Draw the circuit diagram of a push-pull ampli er and explain how even har-
monics are eliminated.
(c) Derive the relation between gain with feed back and without feedback.[6+6+4]

7. (a) Explain the e ect of temperature on
i. i/p bias current
ii. i/p o set current
iii. i/p o set voltage.
(b) Explain in brief the applications of OP-AMP. [8+8]

8. (a) Give the Boolean functions: F= xy + x y +y z
i. Implement with only OR and NOT gates.
ii. Implement with only AND and NOT gates.

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Code No: R05012302
Set No. 2
(b) Explain the principle of master-slave JK ip- op.
(c) Find the complement of given function and reduce it to a minimum number
of literals.(BC +A D) (AB +CD ). [6+5+5]

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Code No: R05012302
Set No. 3
(Bio-Technology)

1. (a) Derive an equation for the total power consumed in a three phase circuit. Will
it depend on the type of load connected?
(b) Three identical impedances 10 53 10 are connected in delta to a 3-phase,
240 volt balanced supply. Find the line currents and power consumed. [8+8]

2. (a) Show that single phase induction motors are not self starting.
(b) Explain the construction and working principle of any type of 1-phase induc-
tion motor. [8+8]

3. (a) Explain how an n-type semiconductor is formed. Name di erent donor impu-
rities used.
(b) i. Find the conductivity of intrinsic silicon at 300 0 .
ii. If donor impurity is added to the extent of 1 impurity atom in 108 silicon
atoms, nd the conductivity. It is given that at 300 0 ,
i = 1 5 × 1010 3 p = 500 2 n = 1300 2 . [4+4+8]

4. (a) Sketch typical SCR forward and reverse characteristics.
(b) Identify all regions of the characteristics and all important current and voltage
levels.
(c) Explain the shape of the curves in terms of the SCR two transistor equivalent
circuit.
(d) Explain why always silicon but not Germanium is used in the construction of
SCR.
(e) Obtain the expression for total current through SCR and Triac. [4+3+3+3]

5. (a) Draw the circuit diagram of a xed 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 = 50 is used in a CE circuit with CC=10 V, C =
2K . The bias is obtained by connecting a 100 K resistance from collector
to base. Assume BE=0 V. Find

i. the Quiescent point
ii. the Stability factor S. [8+8]

6. (a) Compare the three transistor ampli er con gurations with related to AI , Av,
Ri and R0.

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Code No: R05012302
Set No. 3
(b) For the circuit shown calculate AI, AV , Ri and R0 using approximate
h-parameter model. Assume hfe = 50, hie = 1100 , hoe = 25 A/V, hre =
2.5 × 10 4 as shown in the gure 6b. [16]

Figure 6b
7. (a) Draw the circuit diagram of Wien bridge oscillator using BJT. Show that the
gain of the ampli er must be at least 3 for the oscillations to o ccur.
(b) For the xed-bias Ge transistor, n-p-n type, the junction voltages at satura-
tion and cuto one in active region, may be assumed to zero. This circuit
operate properly over the temperature range -50 oC to 75 oC and to just start
malfunctioning at these extremes. The various circuit speci cations are: CC
= 4.5V, BB = 3volts, fe=40 at -50 oC, and fe =60 at 75 oC, CBO = 4
A at 25 oC and doubles every 10 oC. Collector current is 10 A. Design the
values of c1, 1 and 2. [8+8]
8. (a) Explain the following switching circuit in binary logic notation as shown in
the gure8a

Figure 8a
(b) De ne a register. Construct a shift register using S-R ip- ops and explain
its operation.
(c) Convert the following numbers:
i. (101101. 101101)2 decimal number
ii. (5345)10 to binary number. [4+6+6]

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Code No: R05012302
Set No. 3

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Code No: R05012302
Set No. 4
(Bio-Technology)

1. (a) Determine the voltage VAB in the circuit shown in the gure 1a

Figure 1a
(b) Find the power dissipated in 40 resistor of gure 1b shown. [10+6]

Figure 1b
2. (a) With a neat sketch explain the construction of a D.C. machine.
(b) Explain the principle of operation of D.C generator. [8+8]

3. (a) i. Find the resistivity of intrinsic silicon at 300 0K. It is given the i at 300
0K in silicon is 1 5 × 1010 3 and p = 500 2 - n = 1300-
2-
ii. If an acceptor impurity is added to the extent of 1 imputrity atom in
2 × 108 silicon atoms, nd its resistivity.
iii. If a donor impurity is added to the extent of 1 impurity atom in 5 × 107
silicon atoms, nd its resistivity.

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Code No: R05012302
Set No. 4
(b) Prove that the concentration of free electron in an intrinsic semiconductor is
[12+4]
given by = c (Ec Ef )/KT

4. (a) The half wave recti er shown in the gure 4a is fed with a sinusoidal voltage
V=20 sin100t.
i. Sketch the output waveform.
ii. Determine the DC output voltage assuming ideal diode behaviour.
iii. Repeat the calculations assuming the simpli ed diode (silicon) model.

Figure 4a
(b) Draw the circuit diagram of full wave recti er having two diodes and explain
its operation. [8+8]

5. (a) Draw the emitter characteristic of UJT and explain the shape of the curve
qualitatively. Mention di erent regions of operations.
(b) Draw the circuit of a relaxation oscillator and explain its operations. Mention
its applications. [8+8]

6. (a) Compare the di erences between voltage ampli ers and power ampli ers.
(b) Show that the maximum theoretical e ciency of class B push-pull ampli ers
is 78.5%.
(c) Draw the circuit of a transformer coupled power ampli er and explain its
operations with help of load-line analysis. [4+6+6]

7. (a) Draw the circuit diagram of Wien bridge oscillator using BJT. Show that the
gain of the ampli er must be at least 3 for the oscillations to o ccur.
(b) For the xed-bias Ge transistor, n-p-n type, the junction voltages at satura-
tion and cuto one in active region, may be assumed to zero. This circuit
operate properly over the temperature range -50 oC to 75 oC and to just start
malfunctioning at these extremes. The various circuit speci cations are: CC
= 4.5V, BB = 3volts, fe=40 at -50 oC, and fe =60 at 75 oC, CBO = 4
A at 25 oC and doubles every 10 oC. Collector current is 10 A. Design the
values of c1, 1 and 2. [8+8]

8. (a) Convert the following numbers:
i. (1431)10 to base 2.

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Code No: R05012302
Set No. 4
ii. (53 1575)10 to base 2.
(b) Implement AB+C D = F with three NAND gates. Draw the logic circuit.
(c) Prove that the NAND Gate is a universal gate.. [8+4+4]

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12302 Basic Electrical And Electronics Engineering

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