Part - A (Objective test items) -JANUARY - 2009

Q:1. In the figure you will see one type of filament used in incandescent lamps.

        a) which type of filament is shown in the figure?

        b) What is the material used for the filament?

Ans:1. a) Coiled oil filament.        b) Tungsten.

Q:2. A 3-phase induction motor driving a planing machine is found to be getting too much hot.

        What are the possible reasons for this effect, with respect to supply lines?

Ans:2. 1) Single phasing in the 3 phase supply.   2) Low supply voltage.

Q:3. Wire stripper has a series of sharp openings in its scissors blade to fecilitate stripping of wires

        of different sizes.

     

       The correct method of using wire stripper.......

Ans:3.  The gauge size og the wire must match with the opening in the wire stripper.

Q:4. In the figure part of a fluorescent lamp circuit is shown.

        a) What is the name of this part?

        b) How it is connected inltially at the time of starting?

Ans:4.  a) starter   b) In series with the heating elements.

Q:5.  In electrical insulation work supply to each point is provided through a control switch. Four 

         methods are generally adopted for this.

         Looping out from switch and looping out from switch and ceiling rose are tow such methods.

         What are other two methods?

Ans:5.  a) Looping out from 3 plate ceiling roses.
            b) Looping out from junction boxes.

Q:6.  A old resistor has the following colour bands:

        1st band     :   Red             ;        2nd band    :   Green
         3rd band   :   Orange        ;        4th band     :   Gold
         Calculate
         a) The exact value R (in Ω ) of the resistor.
         b) The range of tolerance ∆ R (in Ω from - to).

Ans:6.  a) Red  Green  Orange  Gold
                      2         5           1000         ± 5%    ; R= 25,000  Ω with   ± 5% tolerance
               b) From 23.750 Ω to 26.250 Ω     ; 5% of 25,000 Ω = 1250 Ω
                    Minimum Resistance value = 25,000 Ω - 1250 Ω = 23,750 Ω
                    Maximum Resistance value = 25,000 Ω + 1250 Ω = 26,250 Ω

Q:7.  Domestic mixers / liquidizer generally use universal motor, and it has two windings.

          a) What are these windings?
          b) How they are connected together?

Ans:7.  a) Armature windings are field winding
               b) The two windings are connected in series

Q:8. When the machines  are coupled, they should be properly aligned.

          State tow operations which are to be carried to confirm proper alignment.

Ans:8.  a) Levelling off the centre lines of shafts
              b) Aligning shafts eliminating radial and axial displacement.

Q:9. In a 3 phase motor one of the phases, which is not connected through NVC of starter, is opened
         during running.

         What will be the immediate effect on the motor operation?

Ans:9.  It will continue to run.

Q:10.  In 3 phase 415 v  induction motor has 3 terminals for connecting it to supply.  Whether the
          motor is connected in star or in delta. From the history sheet you get the resistance value 
          of each phase as 8.5 ohms and the motor is rated for 415 v. 

         How would you confirm whether the motor is connected in star/delta connection without 
         dismantling the motor?

Ans:10.  By resistance measurement across any two terminals.
                 If the measured value is 17Ω the motor is star connected.
                 If the resistance measured value is less than 6Ω the motor is delta connected.

Q:11.  There are three basic ways for extinguishing fire.
             One  way is by cooling (reducing temperature).

             Name are the other two tests?

Ans:11.  a) By starving the fire by removing fuel.
                 b) by smoothening ( Isolating fire from supply of oxygen by blanketing)

Q:12.  Four tests are conducted before commissioning any electrical appliances.
             Insulation resistance test and Earth continuity test are two tests.

             What are the other two tests?

Ans:12.  a) Continuity test of element.     b) continuity test of power cord

Q:13.  DC is generated by rotating conductors (armature) in magnetic field.

             How dies AC generation differs from DC generation?

Ans:13. AC can be generated either by rotating field or rotating armature.

Q:14.  The mixee found to be operating erratic and running at different speed.

             How you will solve the problem?

Ans:14. a) check the cord for intermitter break, repair or replace the cord.
                b) Check the connection of the socket and plug terminals and tighten them.
                c) Check the spring tension brushes and replace the brushes.
                d) The switch may be defective, replace the switch.

Q:15.  While testing series field and armature winding of a DC compound machine for continuity 
             with AC supply, you should be careful not to touch shunt field terminals.

             why you should not touch shunt field terminals while testing?

Ans:15.  Induced voltage due to mutual induction in shunt field gives severe shock.

Q:16.  Speed of sling-ring induction motors can be changed by varying rotor resistance.
             Due to certain disadvantages this method has limited application.

             What are the disadvantages?

Ans: 16.  More power loss in Rotor circuit, Power circuit also reduces, Low efficiency.

B- Part - January - 2009

   Q:1. a) state ohms law?
             b) what  is the power input  to an electric heater that draws 3 amp from230 volt supply source ? 
              c)  what is emf? how it can be calculate?
Ans:) see jully 2006 ans no :1a
              p) p=230 x3a=690w
the power input to the electric heater is 690w
               c) the force which causes current to flow in the circuit is called emf its symbols is E and is measure in volts(V)
=v ate terminal of source3s of supply +voltge drop in the source of supply(or) emf= v+ir
Q:2  .a) state the three essential forces required for an indicating instrument.
           b) state the principle of a permanent magnet moving coil (pmmc)instrument.
           c) explane the clipping error in an energy meter.
Ansa) the flowing 3 force areessential requirement of an indicating instument for its satisfactryoperation they are
i.deflecting force
ii.controling force
ii.damping force
             b) see jully 2008 ans no:2a
               c) in som meters  the disc rotets continuously  

Part-A(Objective Test Items )2005

Q:1 .You have taken four readings from a earth resistance testers,placing the spikes at different position 

        around the electrode under test . Distance between electrodes is the same for all the test. The
        measured values are 2.8 ohm 2.1 ohm 2.5 ohm and 1.6 ohm.

        Determine the value of earth resistance.

Ans:1. Total earth resistance

           =2.8+2.1+2.5+1.6 ohm

           =9 ohm

          Average value=9 ohm/4=2.25 ohm

Q:2. The statically induced emf has a polarity which opposes the voltage that created it.

        What is the other name by which this induced emf is know as?

Ans:2. Counter emf (Back emf).

Q:3. To identical 3 phase induction motors in good condition of same HP,voltage, frequency and speed
        are connected to the rated supply voltage. On no load you notice one motor is drawing 1.6 A and
        the other 4.8 A.

       What is the reason for the above current different?

Ans:3. Winding of motors are connected in different ways. Motor drawing 1.6 A is connected in star.Motor

           drawing 4.8 A is connected in delta.

Q:4. What is the method of heat transfer accomplished in a

       a) Hot water boiler.

       b) Electric iron.

Ans:4. a) Convection.

           b) Conduction.

Q:5. After rectifying the short circuit in a electric toaster you have to replace the blown out fuse. The old
        fuse was rated for a current of 1 A.

        a)What is the function of the fuse in normal operation?
        b)What will happen if you use a fuse with 0.3 A?

Ans:5. a) A fuse most not open the circuit under normal operating conditions.
           b) A 0.3 A fuse will open the circuit immediately after you switch ON the toaster as the operating 
              current in the circuit is higher than 0.3 A.

Q:6. State the device used for coarse excess current protection.

Ans:6. Re-wirable type fuse.

Q:7. Apart from high mechanical strength, the metal conduit system of  Wiring has one definite 

        advantage over the PVC conduit system.

       What is the advantage with respect to electrical protection?

Ans:7. Metal conduit also functions as earth continuity conductor.

Q:8. Sheet metal edges of thin gauges are made by hem.

        State any two purposes of the hem in sheet metal work?

Ans:8. a)Hem stiffens the sheet of metal and improves mechanical strength.

           b)Hem prevents sharp edges.

           c)prevents damages to the edges.

Q:9. From making light punch  marking a particular type of punch is used.

         What is the name of punch and its angle of point?

Ans:9. Prick punch. Angle of point 30 degree or  60 degree

Q:10. The amount of current flow in pure resistive circuit on AC is influenced by five factors. Among 

           the five factors three factors are DC Resistance, Eddy current and Hysterisis.

           Name two other factors.

Ans:10.  a)Skin effect.

              b)Dielectric stress

Q:11. There are different methods of connections in domestic installation.Which method is shown 

           in the figure?

Ans:11. Loop-in method.

Q:12. You are connecting a 3 phase induction motor. If you connect starting ends of all the three 

          winding together and give three phase supply to other three ends, which type of connection 

          you have made.

Ans:12. Star connection.

Part B     

Q:1.  a) Name the active chemical substance used in lead acid battery.

       b) State common defects of a lead acid battery.

Ans:1. a)

           i) Lead peroxide (Pbo₂)

          ii) Spongy lead (pb)

         iii) Diluted sulphric acid  (H₂SO₄)

       

       b) Common defects on the lead acid battery.

       i) Sulphation on active plates 

      ii) Buckling of plates

      iii) Sedimentation/Shedding at the bottom of container

      iv) Internal short circuit.

Q:2.  a) A.D.C shunt generator when started up does not build up its voltage. State the possible

            causes for its failure.

         b) Explain why the P.D at the terminal of shunt generator falls as the load increased. What 

             are the factors responsible for this fall in P.D?

Ans:2. a) the shunt generator fails to build up voltage due to 

           i) Absence of residual magnetism

          ii) The field circuit may be reversed.

          iii) The shunt field resistance above the critical value (too high) and do not produce appreciable 

               flux to initiate the build up process.

         iv) Imperfect brush contact on commutator.

         v) The prime mover rotates opposite to the marked direction and speed may be too low.

       b) The voltage developed by a shunt generator is dropping on load due to 

       i) Increased IR drop

      ii) Increased Armature reaction

      iii) Decrease in PD across field terminal due to the above two reasons.

Q:3.  a) Briefly explain the working principle of an induction motor.
        b) What is meant by slip in an induction motor?
        c) A 5 KW, 50 Hz, 6 pole slip ring induction motor runs at 960 r.pm calculate.
        i) sync. speed   ii) % slip

Ans:3. a) Induction motor operates on the principle of faraday's laws of electromagnetic induction. The 
           stator winding is connected to the AC supply which produces a rotating magnetic field . Due
           to this field an emf is induced in the rotor conductors by electro magnetic induction and hence
           the name induction motor. The flux produced by the rotor currents makes the rotor rotate. The 
           direction of rotation is same as the of rotating magnetic field of  the stator. The speed of the rotor 
           is slightly less than the speed of the rotating magnetic field.
     
          b) The difference between synchronous speed (Ns) and actual rotor speed (N) is known as
              slip. It is expressed as percentage of synchronous speed Ns,
              % slip=(Ns-N)/Ns=100

         c) i) f = PN/120 = N = f.120/P
                = 50 x 120/6 =1000
                synchronous speed= 1000 r.p.m

             ii) % slip = Ns-N/N x 100
                           = 1000-960/1000 x 100
                           = 4%

Q:4. a) What is power factor?
        b) Why current of 10 amps flows in a circuit whit 30 degree lag, when the applied voltage is 100
             volts. Find the resistance and reactance of the circuit.

Ans:4. a) Cosine angle subtended between voltage and current
               P.F=Resistance/impedence (or) P.F=True power/Apparent power

               b) I=10 Amps
                   Thita=30 degree lag
                    v=100 volts
                    impendence=(z)=V/I=100/10=10 ohm

                    P.F=cos thita= T/Z; Cos30 degree R/10; 0.866=R/10                    R=8.66 ohm

                    Z=Root R sq + Xl sq
                    Xl = Root zsq-Rsq= Root 10sq - 8.66sq =5 ohm
                   Inductive Reactance = (Xl)=5 ohm

Q: 5. a) Why are the transformers used in distribution system?
         b) Why are thir neutral earthed on the secondary side?

Ans:5 a) To step doen the 11 kv into 440 volt which is suitable to conect 3 phase power loads and single 
              phase lighting loads distribution transformer is used.

         b)  i) Transformer neutral point is earthed to restrict the voltage of live conductors whit repect to 
                 the general mass of earth to a value consistent whit the insulation level.
              ii) To limit the supply voltage fluctuation.

Q:6. a) What are  the different method of transistor amplifier configuration?
        b) Draw a typical circuit whit voltage divider biased PNP transistor amplifier which has phase
             invertion.

Ans: 6.a) 
           i) Common emitter amplifier
           ii) Common base amplifier
           iii) Common collecttor amplifier
          b)
              Common emitter amplifier.
             

           

    

  

        

Part-A(Objective Test Items) July 2008

Q:1. There are different shape of earth electrodes like pipe, plate, rod and grid.

        Which shape of earth electrode used in generating plant?

Asn:1. Plate.

Q:2. After replacing the defective capacitor, the fan motor is still running slow at rated voltage. Bearing 

        and fan blades are found in good conductor.

        What could be the reason for the above defect?

Ans:2. Fault in windings.

Q:3. In which unit AC voltage for long distance transmissions measured as per IE rules?

Ans:3. KV.

Q:4. Figure illustrated is for a typical field tapping method of speed control for a universal motor.

        In which position of the switch the speed will be

        a) High (full speed)  b) Low

Ans:4. a) Position A for high speed.

          b) Position C for low speed.

Q:5. When the tube light switch is "NO", the filaments of the tube at ends light, but the full illumination

        is not taking place ,When a person keep his to hands at the ends of tube and moves the hand 

        to the center the tube fully.

       The reasons for such defect are low supply voltage, defective starter and ............

        Give two more reasons.

Ans:5. Weak active  material due to aging, loose contacts, week filament and choke is partially shorted.

Q:6. Sometimes you see the disc of an energy meter rotating slowly though there is no load 

       while its pressure coil is energised.

       One of the reason for this slow rotation is over compensation for friction.

      Mention two more reasons.

Ans:6. a) Grouping error is due to the breaking  magnet not properly adjusted.

          b) Alignment of disc between the pins.

Q:7. Before commissioning any new electric appliances four tests should be performed.

        Continuity of the element and test for supply.

       State the other two tests.

Ans:7. a) Insulation resistance test.

           b) Earth continuity test.

Q:8. State the possibilities for a change  in the polarity of the terminal voltage of a DC generator?

Ans:8. a) Change in direction of rotation of prime mover.

           b) Change in the direction of the field current. 

Q:9. In a DC relay when the coil is energized  it actuates the relay contacts.

      What is the effect on the relay function if the polarity of supply to the relay coil is changed?

Ans:9. Relay functions normally (polarity reversal of supply has no effect on the function of the relay )

Q:10. Starters are needed for switching on DC motor because of the high starting current.

         State two reasons for the high starting current

Ans:10. Back emf zero and the resistance of the armature is very small.

Q:11.You have  to measure the current drawn by an induction motor without interrupting the circuit.

         a) What instrument will you use ?

         b) State the principle on which it works?

Ans:11. a) Clamp on meter or tong Tester.

             b) Mutual induction.

Q:12. For terminating a cable in to screw on terminals the conductor should be looped.

         What is the tool  used for  looping the conductor ?

         In what direction the loop should be placed in to the screw for termination?

Ans:12. a) Round rose plier.   b) Screw tight direction .

Q:13. a) Line voltage in a 3 phase system is referred to  the voltage measured between..........

          b)In which type of connection line voltage is equal to phase voltage.

Ans:13. a) Between two phase.

             b) Delta connection.

Q:14.  A 200 V, 2 KW DC motor has an efficiency of 0.8 at full load.

Ans:14. Motor output at full load =2000 W

             n=80%

            Input = output/efficiency x 100 = 2000/80 x 100 =2500 W

            Current = W/V = 2500/200 = 12.5 A

Q:15. The speed of squirrel in DOL starter may be due to improper voltage , dirty pole faces and 

          defective spring in the NVC housing. You find all the above conditions are ideal and still the

          problem persists.

         What could be the other possible reason?

Ans:15. No change in speed even load varies.

Q:16. Chattering noise in DOL starter may be due to improper voltage,dirty pole faces and defective
          spring in the NVC housing. You find all the above condition are ideal and still the problem persist.
       
         What could be the other possible reason?

Ans:16. Broken pole shading ring.

Q:17. The small voltage fluctuation in the output of the rectifier is called ripple.

          What is the ripple frequency of full wave rectifier?

Ans:17. 2f input.

Q:18. a) What is the purpose of transformers in regulated power supplies?
          b) On what factor the output current regulated power supplies depend?

Ans:18. a)Stepping down AC voltage to the required AC voltage.
             b) Load regulation.

Q:19.  Universal motor control circuit is shown in the figure.

          a) What is the function of the resistor R?
          b) What are the consequences of a high and low value of resistance R with respect to speed
               of the motor?

Ans:19. a) It varies the supply.
             b) High value of resistance-slow speed
                 Low value of resistance- High speed

Q:20. Opening the switch of an inductive circuit sets an arc across the switch contacts due to large
          voltage induced and stored energy magnetic field.

          The arc is suppressed in such circuits by connecting........
           A)  a capacitor across the supply.
           B)  a capacitor across the switch contacts.
           C)  arcing horns across the switch contacts.
           D)  another small inductor across the switch contacts in reverse direction

Ans:20. B) a capacitor across the switch contacts.

Q:21. Every appliance should be tested for insulation resistance before commissioning. For a water
          heater the insulation resistance should not be less than..........

        A)  1 Meg ohm
        B)  2 Meg ohm
        C) 0.5 Meg ohm.
        D)  0.25 Meg ohm

Ans:21.  A) 1 Meg ohm.

Q:22. As a precautionary measure the heating element used in heaters, electric iron and water heaters
          should not attain a temperature more than......

          A)  335 degree
          B)  635 degree.
          C)  735 degree.
          D)  1035 degree.

Ans:22. D) 1035 degree 

Q:23. When a house wife accidently touched the metal part of the handle of a kettle. Which was
           kept 'on'. She received an electric shock.

           The reason is........
           A) The fuse wire in the circuit is of higher capacity
           B) The kettle is not earthed
           C)There is no water in the kettle
           D) The safety plug has become defective.

Ans:23. B) The kettle is not earthed

Q:24. What is the value of resistor in the circuit shown and its power rating you would select
          for this function?

          A) 2 W, 3.2 k ohm
          B) 2 W, 6.4 K ohm
          C) 4 W, 3.2 K ohm
          D) 4 W, 6.4 K ohm

Ans:24. D) 4 W, 6.4 K ohm.

Q:25. Tong tester is used to measure the current in AC circuit without interrupting the circuit.
          For measurement the split core is clamped on to the insulated current carrying conductor.

          Looping of conductor passing through the split core is used some times.
          What will be the reading for a selected range if the conductor is looped (double pass)?

          A) Double the current which pass through the conductor.
          B) 4 times (i.e., 2^{2) the current which pass through the conductor.
          C) Half the current which pass through the conductor.
          D) Same as the conductor current.}

Ans:25. A) Double the current which pass through the conductor.

Q:26.  The direction of rotation of a permanent capacitor motor can be reversed by interchanging the ......

           A) Centrifugal switch terminals
           B) Auxiliary winding terminals
           C) Capacitor terminals
           D) Supply terminals

Ans:26. B) Auxiliary winding terminals.

Q:27. Which type of fault is tested in the above figure?

          A)  Testing the continuity of each winding.
          B)  Testing for open circuits.
          C)  Testing for grounds.
          D)  Testing the resistance value between each winding.

Ans:27. C)  Testing for grounds.

Q:28. You have to change the defective induction motor of a machine. The available motor is of a
           higher capacity than the existing one.

           What is the effect of using a higher capacity motor?
           A) The new motor will be overheated.
           B) The new motor is better suitable for this work.
           C) The efficiency and the power factor will become low.
           D) The new motor has a longer useful working life and efficiency.

Ans:28. C) The efficiency and the power factor will become low.

Q:29. Brush tension in a DC generator play very important role in its performance.
   
          Excessive brush tension may.........
          A) Slow down the speed of the machine
          B) Decrease the output voltage
          C) Increase the output voltage
          D) Overheat the commutator and wear out the surface.

Ans:29.  D) Overheat the commutator and wear out the surface.

Q:30. What are the ON / OFF terminals of a transistor when it is operated as a switch?

          A)  Collector to base
          B)  Collector to emitter
          C)  Base to collector
          D)  Emitter to base.

Ans:30. B)  Collector to emitter

Q:31. Which colour wire is recommended for earth connection as per ISI code?

          A) Red
          B) Green
          C) Black
           D) Blue

Ans:31.  B) Green

Q:32. If single phasing occurs during running of a 3 phase motor, What is the effect on motor
          performance?

          A)  Motor will run as 2 phase motor and performs normally.
          B)  Will continue to run on 2 phases but fails to take load.
          C) Continue to run on 2 phases, draws excess current,winding likely to burn.
          D)  Run at reduced sspeed and can take only 2/3 of the load

Ans:32.  C) Continue to run on 2 phases, draws excess current,winding likely to burn.

Q:33. The precision of measurement depends on the range of the instrument selected.

          What is the general rule for selection of range of instrument?
          Measured value should be.........
          A) Above the mid-scale
          B) Below the mid-scale
          C) On the mid-scale
          D) Exactly on full scale

Ans:33. A) Above the mid-scale.

Q:34. Rotor resistance starters are used with wound rotor induction motor,
          When the motor is running the resistance in starter are........

           A) Shorted
           B) Open circuited
           C) Connected in delta
           D) Connected in star

Ans:34. A) Shorted

Q:35. How the PF meter is connected in the motor circuit?

          A) Fixed coil in parallel with the supply and moving coil in series with single phase motor.
          B) Fixed coil across the motor and moving coil across the supply.
          C) Fixed coil in series with motor and moving coil across the supply.
          D) Both Fixed coil and moving coil in series with the motor.

Ans:35.    A) Fixed coil in parallel with the supply and moving coil in series with single phase motor.

Q:36.  You have to change the defective motor of an electric locomotive.

           Which type of motor would you choose?
           A) DC differential compound motor.
           B) DC shunt motor.
           C) DC series motor.
           D) Separately excited motor.

Ans:36.  C) DC series motor.

Q:37. Match the materials with the parts of U.G cable

          Materials
        1) Copper
        2) Lead (or) Lead Alloy
        3) Steel wire
        4) Aluminium
           Parts of Underground cable
        A) Core
        B) Metallic sheath
        C) Armouring

Ans:37. 1. [A]  2. [B]  3. [C]  4. [A]

Q:38. Match the explanations with the mandatory sings.

      Explanations

      

      1.   Wear hearing protection.

      2.   Use adjustable guard.

      3.   Wear safety harness

      4.   Wear safety belt.

      5.   Wear foot protection

      Mandatory sings

Ans:38. 1. [B]  2. [A]  3. [D]  4. [D]  5. [C]

Q:39. Match the different toraues with the labeled points in the graph.

         Name of the torque
         1)  Breakdown torque
         2)  Starting torque
         3) Full load torque
         4) Rated torque
         5) Torque at no load operation
        Torque-speed characteristic

Ans:39. 1. [B]  2. [A]  3. [C]  4. [C]  5. [D]


Q:40. Match the type of instruments with the measurements.

          Instruments
         1) Pyrometer
         2) Hydrometer
         3) High rate discharge tester
         4) Tong tester
         5) Thermo-couple with a calibrated millivoltmeter
         Measurements
        A) To measure current without interrupting the circuit
        B) Specific gravity of electrolyte of a car battery
        C) To make, sure test of a battery after charging
        D ) Temperature of a furnace

Ans:40. 1. [D]  2. [B]  3. [C]  4. [A]  5. [D]

     
       

              

         
   
 
       
     

                   

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