EDCA- 2, EM-2 question papers

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2015 

  May / June

Attempt for 2 marks

- In order to achieve high voltage amplification in voltage amplifier which main features are incorporated in it.

- Power amplifiers generally use Transformer coupling because Transformer permits.....

- list the advantages of tuned amplifier.

- the basic purpose of applying negative voltage feedback is to........( Increase gain or reduce distortion or keep normal temperature )

- can applying negative current feedback to an amplifier its output impedance is is impedance is.......( Increases, decreases, same as before) 

- for an oscillator to properly start, the feedback loop must initially be.........( One, greater than one, smaller than one )

- wien bridge oscillator uses......,feedback ( only +ve, only -ve, both +ve and -ve )

- draw the circuit of positive clipper with the bias.

- which component is clamping circuit effectively acts as a battery.

- the multivibrator which generate square wave of its own is the ........ multi vibrator.

- AC power supplies are categorised into three types namely.........

- in ideal op amp have........ Voltage gain,........... Input impedance and........ Output impedance.

- show the circuit to obtain an And gate from Nand Gates.

- the only function of not gate is to.........( Stop a signal/ invert input signal/ act as a universal gate)

Attempt for four marks

- Compare beta, Rc, coupling, input voltage, collector current, power output impedance of voltage and power amplifier.

- Draw the circuit to illustrate the principle of negative current feedback and obtain the expression for current gain.

- draw the circuit of a simple transistor amplifier and explain its working.

- draw the circuit of a phase shift oscillator.

- draw the block diagram of a multivibrator to illustrate its principle and show the output across the 2nd stage transistor.

- draw the circuit of an op-amp integrator with a square wave input and corresponding output.

- state the single variable basic theorems with respect to logic gates.

- draw the basic block diagram of a DC power supply with proper labelling.  State broadly its three main circuits.

Attempt for 20 marks

- a. Describe the working of a class a single ended power amplifier with the help of circuit diagram.

b. discuss the basic principle of complementary symmetry push pull amplifier and explain its operation.

- a. explain the working of tuned class C amplifier.

b. discuss the operation of emitter follower. Show that its voltage gain is approximately one.

- a. what is a darlington amplifier? Discuss its circuit analysis and obtain the expression input impedance.

b. Explain the operation of Hartley oscillator and obtain the expression for feedback fraction.

- a. Describe the working of a transistor bistable multivibrator.

b. What is clipping circuit? Discuss the operation of combination clipper with its waveforms.

- a. discuss the working of voltage follower op amp. Show that its closed loop voltage gain is 1.

b. draw the systematic circuit diagram of typical step down SMPS and discuss its operation.

2018

Attempt for two marks

- an ideal voltage amplifier has...... Input resistance and......... Output resistance.

- what do you mean by an electronic oscillator.

- what is the criteria for oscillation for a positive feedback amplifier.

- give the basic principle of operation of tuned collector oscillator.

- perform the binary subtraction 1101-111.

- explain the term bit and byte. What are the advantages of using 0, 1 notation in the binary system.

- what is the logic symbol for an And gate and OR gate.

- describe the use of an op-amp as an inverting amplifier.

- explain transistor as a switch.

- what are the advantages of using op amp

- feedback always increases the gain of an amplifier. is it true or false.

- define the half power frequencies.

- plot the frequency response curve of RC coupled amplifier

- what do you mean by conversion efficiency of a power amplifier.

Attempt for four marks

- obtain expressions for the voltage gain of an RC coupled amplifier in the low and high frequency ranges.

- show that negative feedback improve the stability of the gain of an amplifier.

- discuss the amplitude stability of the wein bridge oscillator.

- what is  Barhaunch criterion? State the basic condition for oscillating in a feedback amplifier.

- state the characteristics of an ideal op-amp.

- draw an emitter follower circuit and state its applications.

- give the logic symbol, Boolean expression and truth table for an XOR gate.

Attempt for 20 marks

- a. Designer 2 input XOR gate with the help of nand Gates and nor Gates.

b. Explain the working of an astable multivibrator.

- a. Give the circuit diagram of Hartley oscillator and explain its operation.

b. Describe the working of a RC differentiating circuit.

- an open an inverting amplifier has a input resistance of 10 kilo ohm and a feedback resistor of 50 kilo ohm, if the input voltage is 0.5 volt, find the output voltage and the input current.

- a. what do you mean by conversion efficiency of a power amplifier? How does efficiency changes from class A to class C through class AB and class B?

b. Discuss the working of colpitts oscillator.

- write short notes on such topics

a. Piezoelectric crystal

b. Shunt clipping circuit

c. Open as voltage follower

d. Difference between voltage and power amplifier.

EXAM POINT OF VIEW

Important Topics

-  Difference between voltage and power amplifier. 

- Classification of power amplifier ( class A, class B, class C )

- Definition of heat sink

- Push pull Amplifier, Complementary Push pull.

- ( very important topic )

Feedback, positive, negative , advantages , gain of negative and positive feedback as an oscillator.

- Define sinusoidal oscillator. Difference between oscillator and alternator.

-  Different types of oscillator .( most important )

- Tuned voltage amplifier, resonance , frequency response.

- Switching and wave switching circuits ,(multivibrator clipper, clamper),  ( most important ), differentiating and integrating circuit.

- Special power supplies ( CVT, SMPS, UPS, ) most important.

- Characteristics of op amp ( most important)

Op amp topic with derivation . 

- All gates ( most important) with truth tables  

And conversions if you want one question from it.

For such topics visit their answers from blog notes.

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                            ELECTRICAL MACHINE - II
                                     3K-DFSN-01

Attempt for 2 marks

- explain the turn and coil span factor in connection with alternator armature windings.

- draw neat sketches of cylindrical and silent pole type rotors.

- define slip speed.

- write any two advantages of ground rotors used in 3 phase function motors.

- what is synchronous speed?

- the highest speed at which a 60 hertz alternator can be operated is............

- define slip in an induction motor.

- why starters are necessary for starting induction motors?

- what are the causes of hunting in 3 phase synchronous motors.

- what methods are generally used to start the synchronous motors?

- what type of motor would be used in washing machine and sewing machine.

- draw the torque speed characteristic of 3 phase induction motor.

- in a shaded pole motor the reversal of direction of rotation is not possible. Is this statement true or false?

- what is full pitch winding?

Attempt for 4 marks

- draw the circuit diagrams to conduct open circuit and short circuit test on an alternator.

- describe the pitch factor and distribution factor and their interrelationship.

-three phase, 50 hertz, 4 pole induction motor has a sleep 4 percentage. Calculate the speed of motor and frequency of rotor EMF.

- derive the relationship between rotor copper loss rotor input power for three phase induction motor

- prove that the starting torque is proportional to the square of the starter applied voltage in a three phase induction.

- describe repulsion motor in brief.

- what are main features of dol starter?

- explain double cage rotor of a three phase induction motor.

Attempt for 20 marks

- a.  describe the construction and working of a capacitor start single phase induction motor

b. Draw the circuit diagram of a capacitor start capacitor run single phase induction motor.

- a. what are v curves of a synchronous motor? What are the main characteristics of a synchronous motor?

b. Determine the line current, armature current and excitation voltage.

- a. Explain parallel operation of three phase alternator by any one method

b. draw the appropriate equivalent circuit diagram of 3 phase induction motor and draw its torque speed characteristics.

- a. Describe the working of slip ring induction motor starter with diagram

b. Derive EMF equation of a three phase alternator.

-a.  explain determination of regulation of three phase alternator by any one method.

b. Describe no load test and blocked rotor test of three phase induction.

         Another set of Electrical machine-II

Attempt for two marks

- define electric machine

- what is an infinite bus bar?

- in and fractional pitch winding the coil span is less than ........ Electrical degrees.

- explain excitation system of AC generator.

- what is synchronous impedance of an alternator?

- armature reaction for unity power factor is.....

- differentiate round rotor induction system from scroll cage induction motor on the basis of construction.

- write name of the speed control methods of induction motor.

- a shaded pole motor winding coil is normally made of............

- a ceiling fan uses..........motor.

- write the name of wedges in single phase AC motor.

- asynchronous motor behaves like are condenser in........... Excited mode

- for starting a synchronous motor are small........motor is used.

Attempt for four marks

- describe a synchronous motor.

- describe shaded pole motor. Where is it normal used?

- how can a synchronous motor improve its power factor of system?

- what are the methods of cooling of ac generators?

- draw circuit diagram of 3 phase induction motor

- what are the main features of dol starter?

- explain briefly armature reaction in alternator.

- describe no load and blocked rotor test on 3 phase induction motor.

Attempt for 20 marks 

- a. Derive an expression for induced EMF in an alternator.

b. What do you mean by ventilation of turbo alternator? Explain hydrogen cooling.

- a. Explain the method of determining the voltage regulator of an alternator by synchronous impedance method.

b. A 500 V, 50 kVA single phase alternator has an effective resistance of 0.2 ohm. A field current of 15 ampere produces a current of 170 ampere on short circuit and open circuit EMF of 125 volt it. Calculate the full load regulation of 0.5 power factor lagging.

- a. draw the simplest equivalent circuit diagram of an induction motor and draw its torque speed characteristics.

b. A 4 pole, 50 Hz, 3 phase induction motor has a rotor resistance of 0.024 ohm per phase and standstill reactance of 0.6 ohm per phase. Determine the speed at which the maximum torque is developed.

- a. Explain why a single phase motor is not self starting. How will you make it self starting?

b. Explain with sketch the working of universal motor and its uses.

- a. Explain the power angle of characteristic of an alternator

b. Explain the phenomena of V curves of a synchronous motor.

- a. Write a short note on parallel operation of two 3 phase alternator.

b. Write a short note on Star Delta starter of three phase induction motor.

Important Topics

Exam point of view

- ventilation of turbo alternators

- no load and blocked rotor test

- shaded pole motor

- dol starter

- Star Delta star Transformer and auto 

transformer starter

- torque speed and slip speed characteristics

- power loss of alternator

- magnetomotive force method

- leakage reactance, cage and wound rotor

- load characteristics of alternator

- EMF of alternator

- universal motor or repulsion motor

- dark lamp method

- V curve of synchronous motor

- difference between synchronous motor and three phase induction motor

- define hunting, slip,  parallel operation synchronous speed.

- why single phase induction motor are not self starting

- write synchronising power and torque.

- write two reaction theory and infinite Bush

-  What is pitch factor and breadth factor

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