# Canadian Second Class ME  ElectroTech

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ATTEMPT SIX QUESTIONS: THREE FROM SECTION �A� AND ANY THREE OTHERS FROM SECTION �B�

SECTION �A�

1-A. An electric furnace operating off a 240 V supply with an efficiency of 76% raises the temperature of 3 kg of iron from 16 C to 750 C in 20 min. Calculate the:
(i) current
(ii) resistance
(iii) power
(iv) energy absorbed (kWh)
NOTE: Specific heat capacity of iron = 500 J kg -1 K-1

2-A. (i) State the chemical reaction that take place during the charging and discharging of a NICKEL-CADMIUM ALKALINE storage battery.
(ii) A nickel-cadmium alkaline storage battery is discharged at a constant current of 6 A for 12 h at an average terminal voltage of 1.2 V. A charging current of 4 A at 1.5 V applied for 22 h is necessary to completely recharge the battery, Calculate the ampere-hour and the watt-hour efficiencies of this battery.

3-A. (i) Sketch a solenoid indicating the shape and polarity of the magnetic field and the direction of the current to produce this effect.
(ii) What is the effect produced if a soft iron core is inserted into the solenoid.
(iii) A solenoid 75 cm long is wound with 4000 turns of wire. Calculate the magnetic flux density when a current of 2.84 A is applied to the coil.

4-A. Three current of peak values 10 A , 17.32 A and 20 A respectively meet in a common conductor. The 17.32 A current lags the 10 A current by 90 electrical degrees and leads the 20 A current by 60 electrical degrees. Draw a phasor diagram (not to scale) and calculate the value of the resultant current, giving its phase relation with respect to the 10 A current.

5-A. A ship�s electrical service supplied 100 kVA at 440 V and 60 Hz to an induction motor with an inductance of 1 H and an ohmic resistance of 350 ohms. Calculate the:
(i) inductive reactance of the motor
(ii) impedance
(iii) current supplied to the motor
(iv) power factor
(v) power input to the motor (kW)
(vi) size of capacitor ( F) required in the circuit to raise the power factor to 95%

SECTION �B�

6-B. Describe a Synchroscope used when paralleling two alternators. Illustrate your answer.

7-B. Sketch a switchboard for controlling the performance of two-three (3) phase alternators that may be arranged for parallel or simultaneous operation while sharing the electrical load. Your sketch should include all the necessary meter, instruments, regulators, circuit breakers and other protective devices required for controlling of the machines.

8-B. Describe the STAR-DELTA type of starter for a large squirrel cage induction motor. What is the advantage of this method of starting?

9-B. Sketch and describe an electric brake for a cargo winch. What care and attention does it require for safe and efficient operation?

1. What is meant by the terms Electromotive Force and Potential Difference? Explain carefully the difference between them.

2. Three resistances of 5, 3 and 10 ohms are connected in parallel to form one group. This group is now connected in series with a resistance of 3 ohms. The terminal voltage across the circuit is 110. Find the total current flowing and the current flowing through each resistance.

3. What is meant by the terms Direct Current� and A Alternating Current? Explain how the root-mean squared value of and alternating current is obtained by calculating and state the practical importance of this value.

4. What are the chemical magnetic and heating effects of an electric current? Give examples where these effects can be used to advantage in practice and where these effects can be disadvantageous.

5. A steam turbine drives a 300-kilowatt generator and steam is supplied from an oil fired boiler. The overall efficiency of the plant is 7.5%. What is the fuel consumption in lbs., per kilowatt-hour, if the calorific value is 19,500 B.T.Us. Per lb.

6. A pump is driven by an electric motor taking 25 amps., at 210 volts, and whose efficiency is 85%. If the efficiency of the pump is 70 %, how many gals. of salt water will it deliver per min., to a height of 50 ft.? Take 1 cu.ft. of salt water as weighing 64 lbs.

7. Three coils of resistances 5, 10, and 20 ohms are connected in parallel and these in turn are connected in series to a 0.5 ohm resistance. If a voltage of 110 volts is applied across the whole circuit/find the voltage drop across each resistance and the current flowing in each one.

8. An electric heater raises the temperature of 8 tons of oil through 120EF., in 28 hours. The specific heat of the oil is 0.45 and the potential difference across the heater is 220 volts. Find the equivalent ft.lbs. of energy dissipated by the heater, the equivalent horse power, and the current supplied in amperes.

9. An iron wire and a lead wire are connected in parallel. The ratio of the specific resistance of iron to that of lead is as 24 is to 49. The iron wire is 60% longer than the lead and the iron wire is 20% greater in cross-sectional area. Find the percentage current flowing in each wire.

10. A piece of wire is bent into a circle and the ends are joined. Another straight piece of the same wire is now connected as a diameter to the circle and 220 volts is now applied across the ends of the straight wire. If the resistance of the straight wire is 3.5 ohms., calculate the total current flowing through the circuit formed.

11. An electric circuit is made up of one hundred and seventy-five 100 volt 60 watt lamps, and one 20 B.H.P., motor which has an efficiency of 85%. The generator supplying current to this circuit has an efficiency of 90% and is driven by a steam engine whose mechanical efficiency is 85%. Find (a) the output of the generator in kilowatts, and (b) the I.H.P., of the engine.

12. In an electrically heated crucible 12 lbs., of lead at a temperature of 60EF., were reduced to a molten state in 20 min. The heater was supplied with 5 amps., at 110 volts. The melting point of lead is 640EF., its specific heat is 0.031 and the Latent heat of fusion is 10.54 B.T.Us., per lb. Find the efficiency of the apparatus.

13. If a wire of total length >L= and resistance >R= ohms is cut into >n= equal lengths and these are then connected in parallel, prove that the equivalent resistance >RQ= of the circuit is given by; - RQ = R/n5 ohms. A piece of wire of 72 ohms resistance is cut into 2 equal lengths. Find the equivalent resistance if these two lengths are now connected in parallel.

14. A copper conductor 1,000 yd., long has a resistance of 0.5 ohms at 68E F. find the cross-sectional area of the conductor in sq.ins., given that the temperature co-efficient is 0.00393 per 1EC., and the specific resistance at 0EC. = 0.63 x 10 to the -6 ohms per in. cube.

15. A lamp filament is 60 cms., long and has a diameter of 0.04 mm. The specific resistance of the filament when cold is 0.0000165 ohms per cm.cube. When hot under normal working conditions the resistance is 6 times that when cold. If the voltage drop across the lamp is constant at 110 volts, find the current flowing, (a) under normal working conditions and (b) when the lamp is just switched on.

16. In a certain electrical circuit a copper wire and an aluminum wire are connected in parallel. If he copper wire is 30% longer and 10% smaller in diameter than the aluminum wire, find the ratio of the currents flowing in each wire. Specific resistance of copper = 0.63 microhm per in. cube. Specific resistance of aluminum = 1.04 microhm per in. cube.

17. Define the term�s temperature co-efficient� and specific resistance with respect to electrical conductors. Give examples of materials which have negative and constant temperatures co-efficients, and state where the latter can be used to advantage.

18. What physical and electrical properties make copper and aluminum good conductors? What effect has length, cross-sectional area and temperature on the resistance of these conductors?

19. Three conductors of copper, aluminum and tin respectively are connected in parallel ans at 0E C., they take equal currents. What is the percentage of the total current flowing in each conductor when the temperature is 100EC? The temperature coefficients of resistance are;- Copper = 0.00428 at 0EC , Aluminum = 0.0038 at 0 EC, Tin = 0.0045 at 0EC.

20. Define the terms resistance@ and specific resistance@ with respect to electrical conductors. Discuss the physical and electrical properties desirable for electrical conductors and insulators and give examples of material commonly used for these in electrical circuits.

21. It is required to charge a battery of 50 cells connected in series, each having an internal resistance of 0.03 ohm and an average e.m.f., of 2.2 volts. If the supply voltage is 220 and the charging current is 2.5 amps., calculate the value of a resistance to be placed in series with the battery and the percentage power supplied that is wasted in the resistance.

22. The discharge rate of a battery is given by the law;- I to the n times t = K. where I = amps; t = time in hours, n & K are constants. If the battery discharge at the rate of 45 amps for 2.5 hours and on another occasion at 18 amps for 9 hours, find how long it would take to discharge at 15 amps.

23. A battery consisting of 8 cells in series, each having an e.m.f., of 1.4 volts and an internal resistance of 0.3 ohm, is connected to resistance of 4, 8 and 16 ohms, separately at first and then with the three resistances in parallel across the battery terminals. Find the total current flowing in each case.

24. Three batteries connected in series each having an e.m.f., of 1.5 volts and an internal resistance of 0.4 ohms. The batteries supply current to an external circuit of 16.4 ohms resistance. Find (a) potential difference across the external circuit and (b) the potential difference across the first two cells.

25. What quantity of electricity, measured in coulombs, will deposit 10 gms., of copper from a solution of copper sulphate? What current would be required if this process took 1 hour? What weight of silver would be deposited from a silver nitrate solution if the same current flowed for the same time? Electro-chemical equivalent of copper = 0.00033 gms., per coulomb. Electro-chemical equivalent of silver = 0.001118 gms., per coulomb.

26. An ampere is defined as that steady current which will cause 0.001118 gms., of silver to deposit from a solution of silver nitrate in 1 second. An ammeter when connected in series with a silver nitrate meter gave a steady reading of 5 amps. From the experiment the following data was recorded;- time of test = 15 min. Initial weight of cathode = 9 gms. Final weight of cathode = 14 gms. Calculate the error, high or low of the ammeter.

27. Explain the difference between the e.m.f., of a cell and the potential difference across the terminals. In a test carried out on a cell the following results were recorded;- I (amps) 0.5 1.0 1.5 2.0 2.5 p.d. (Volts) 3.5 2.77 2.05 1.33 0.6 - plot a graph of these result and from it find ; (a) the e.m.f., of the cell; (b) the internal resistance of the cell.

28. What weight of copper in lbs., will be deposited from a solution of copper sulphate by a current of 15 amps., flowing for 35 min. Electro-chemical equivalent of copper 0.00033 grams per coulomb.

29. What are the causes of Sulphation, Hydration and buckling of plates in lead-acid batteries? State the remedies for the first two conditions and state why buckled plates are useless for further service.

30. Describe a lead-acid accumulator or storage battery. Give the chemical reactions which take place during charging and discharging of the battery.

31. Two volt meters, one of copper and one of silver, are connected in series and a current is passed through them. If 20 gms., of silver are deposited in a certain time, calculate the weight of the copper deposited during this time. The electro-chemical equivalent of silver is 0.001118 gms., per coulomb and the electro-chemical equivalent of copper is 0.00033 gms., per coulomb. Also find the weight of hydrogen liberated if chemical equivalent of copper is 31.8.

32. Describe a lead-acid accumulator or storage battery. What regular care and attention does this type of battery require and what precautions are necessary if it is to be out of service for several months? How is this type of battery charged?

33. Explain what is meant by the terms electrolyte, :cathode@ and anode@ when used in connection with electrolysis. Given a silver nitrate voltmeter explain how this can be used to measure the value of a steady current passing though the meter.

34. A six pole generator has a useful flux of 7 x 10 to the 6 lines per pole. The armature is lap wound and has 624 conductors. What is the e.m.f., generated if the armature revolves at 1,000 r.m.p.?

35. What is galvanic Action@? What conditions are necessary to promote this effect under practical conditions. Where can galvanic action occur on the hull or machinery of a ship? What steps can be taken to prevent it?

36. Explain what is meant by the terms Electrolysis@. For what commercial purpose can this effect be used? How does this effect differ from Galvanic action?

37. In a d.c., machine the four field coils are in series and each has 2,000 turns. During a continuity test the current is switched on and off at a rate of 0.2 seconds. The induced lines of force are 2.5 megalines which drop to a residual value of 1 megaline. Find the induced volts.

38. State Lenz=s Law. 2 coils X and Y of 600 and 3600 turns respectively are wound on an iron core. A current of 4.5 amps., in coil X builds up a field of 80,000 lines strength in the core. Find the e.m.f. induced in each coil if the current is reversed in 0.02 seconds.

39. Find the force required, (a) in dynes, (b) in gms., and (c) in lbs., to move a conductor 60 cms., long, carrying a current of 130 amps., across a magnetic field of 8,000 lines per sq.cm.

40. A 4 pole motor has a wave wound armature of 0.4 ohm resistance. The armature has 594 conductors and the flux per pole is 0.75 megalines. If the supply voltage is 220 and the motor runs at 1380 r.m.p., find the armature current.

41. Make a sketch of a solenoid coil showing the direction of the current flow in the wire, and then show clearly the lines of force and their direction. Indicate the polarity and state the simple rule used to determine the direction of the lines of force. What would be the effects if a soft iron core was now inserted in the coil?

42. Make sketches of current carrying conductors arranged as ;- (a) a straight wire, (b) a single ring or loop, and (c) a coil or solenoid. On each sketch show clearly the associated lines of force and their direction. In cases (b) and (c) indicate the polarity of the resulting field. State the simple rule used to determine the direction of the lines of force.

43. A spare shaft 5 ft., long is supported athwartships on the deck of a vessel which is steaming at 30 knots. The lines of force due to the earth=s magnetic field have a density of 0.4 lines per sq.cm. What would be the voltage, measured in millivolts, induced in the shaft?

44. With reference to generators explain the meaning of the terms Residual Magnetism, Lines of Force, induction, and Conduction, and state to what parts of the generator they apply.

45. An alternating voltage of r.m.s., value 100 volts is applied to a circuit of negligible resistance and an inductive reaction of 25 ohms. Calculate the r.m.s., value of the current flowing. Sketch the graph of the variation in current and voltage during one cycle of the applied voltage.

46. Why is the r.m.s., value of an a.c., sinusoidal wave used for calculations? Determine (a) the maximum current generated if the r.m.s., value is 4.78 amps., and (b) the frequency if the periodic wee change is 0.03 seconds.

47. The average value of a sinusoidal current wave is 170 amps. Find graphically the value of the current at 0.003 secs.; 0.006 secs.; and 0.008 secs., after the zero value, and increasing positively. The frequency is 50 cycles per sec. The average value is 0.637 of the maximum value.

48. An a.c., current has a wave form from which is an isosceles triangle with a maximum value of 10 amps. Draw a graph of one cycle of this wave form and on the graph draw a curve of the heating effect of the current. Taking 10 mid-ordinate values of the current, for 1/4 of a cycle calculate the r.m.s., value.

49. Calculate the total effective reactance of an a.c., circuit consisting of a coil of 100 millihenry inductance in series with a condenser of 20 microfarads capacitance. The frequency is 50 cycles per second. If the coil has a resistance of 10 ohms find the impedence of the circuit.

50. If a non-inductive resistance of R ohms is connected in series with a pure inductance of L henrys and the voltage drops across each are 200 and 150 respectively, calculate the applied voltage.

51. Given that - i = 20.7 Sin 520t where i - instantaneous value of current and t = time in seconds. Find (a) the frequency (b) the instantaneous value after 0.015 secs. and (c) the maximum value of the current.

52. Define the average value and the root-,mean square value of an alternating quantity. Calculate the average and r.m.s., value for the stepped half wave given;- Milliseconds 1-10 10-20 20-30 30-40 40-50 50-60 Steady current 2 4 6 8 6 4 (Amps) Milliseconds 60-70 Amps 2

53. With reference to a.c., circuit what is meant by the terms resistance, reactance and impedance? A simple a.c., circuit consists of a resistance, an inductive reactance and a capacity reactance, all in series. Explain, with the aid of a vector diagram how the impedance of the circuit is obtained.

54. With reference to an alternating current explain the meaning of the terms frequency, root mean squared value and inductance. State how the r.m.s., value is obtained and why it is used and also state the effects of inductance in an a.c., circuit.

55. An inductive coil in an a.c., circuit has a resistance of 19.5 ohms. If the frequency is 50 cycles per sec., and the voltage is 200, find the inductance of the coil if the current is 10 amps.

56. Find the impedance and power factor of an a.c., circuit consisting of two pieces of apparatus in series. Piece A has a resistance of 2 ohms and an inductive reactance of 14 ohms, and piece B has a resistance of 10 ohms and a capacitive reactance of 6 ohms.

57. The coil of a moving coil voltmeter has a resistance of 5 ohms at 20 EC., and gives a correct full scale reading when a p.d., of 75 millivolts is applied. If the coil is wound with wire which has a temperature co-efficient of 0.0043 per 1EC., find the percentage error in the reading when the temperature is 60EC. State whether the meter is reading high or low.

58. A cable 1,000 yds., long has a resistance of 4 ohms. A fault occurs at C, a point between the ends A and B. on testing it is found that the resistance between A and C, including the fault is 6 ohms. The resistance between B and C, including the fault is 9 ohms. Find the distance of the fault from end A and the resistance of the fault alone.

59. A moving coil ammeter has a resistance of 20 ohms and requires 10 milliamps for a full scale deflection. Calculate the resistance necessary to permit the instrument to be used to read;- (a) currents up to 75 amps. (b) as a voltmeter for voltages up to 35 volts.

60. An ammeter in a circuit has a shunt resistance connected in parallel with it. Prove that the ratio of the line current to the current flowing in the shunt is equal to ;- Ra + Rs Where Ra = resistance of ammeter, Rs = resistance of shunt. Ra

61. Describe, with the aid of a sketch the construction of a moving iron meter, and explain how it functions. Explain how damping is effected with this type of meter. What are the chief advantages and disadvantages of this type of meter?

62. Describe, with the aid of a sketch, the construction of a moving coil meter and explain how it functions. How is this meter connected to the mains when used as a voltmeter and when used as an ammeter?

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64. With the aid of a diagrammatic sketch describe the construction and the principle of operation of a Megger or ohmmeter-testing instrument.

65. Describe a main circuit contact beaker. What provisions are made for protecting against overload, reversed current, an no-volt conditions? How are the contacts protected when the breaker trips open on heavy current?

66. Describe the construction and explain the function of a shunt field regulator as fitted on the switchboard of a ship having two d.c., compound wound generators. By means of a diagrammatic sketch show how the regulator is connected into the generator circuit.

67. With the aid of a simple sketch, describe how earth or ground lights are fitted to a d.c., generator switch-board. Explain carefully how these lights operate, for example in the case of an earth occurring on the positive side of an external circuit. How would you locate and eliminate such a fault?

68. Describe, with the aid of a diagrammatic sketch, a typical switchboard as found on a vessel which has two or more d.c., generators for lighting, heating and power purposes and which can be run in parallel. Indicate all the necessary instruments, switches etc., to be found on the board.

69. Explain the necessity for having equalizing connections between compound wound generators which can be run in parallel. Give, in proper sequence, the steps necessary to start up a compound wound generator so that it may be run in parallel with a similar machine which is already on load.

70. A 30 K.W. generator supplies feed lines 1,000 ft., long, the material of which has a specific resistance of 2/3 microhms per in. cube. If the current density is 1,000 amps., per sq.in., of cross-section, find the percentage efficiency of transmission of power if;- (a) the supply voltage is 110 volts. (b) the supply voltage is 440 volts.

71. Sketch and describe a starter for a d.c., shunt motor. What safeguards are incorporated into the starter to guard against overload and the sudden failure of the shunt field current.

72. In a three wire d.c., distribution system the following loads were between the positive outer and the neutral;- 20 amps., at 100 yds., 60 amps at 150 yds., and 20 amps at 250 yds. Between the negative outer and the neutral there were 20 amps at 100 yds.; 40 amps at 160 yds., and 30 amps at 240 yds. All measurements are from the supply point. Sketch out the system and show the magnitude and direction of the current in each part of the mains.

73. Describe a three-wire system of d.c., distribution which uses one generator. What are the advantages of this system compared with a two-wire system? What is the function of the balancer in a three-wire system?

74. With reference to d.c., distribution systems what is a ring Main. Explain how this type of main functions and state its advantages and disadvantages.

75. To drive a 20 K.W., motor there is a choice between a 220 volt or a 440 volt supply. If the power loss in the transmission leads is the same in either case, what voltage should be used, and what is the percentage saving in copper when compared with the other votage?

76. In a three wire d.c., distribution system the distribution board is 500 ft., from the generator bus bars. The specific resistance of the cable material is 2/3 microhms per in. cube. The cross-sectional area of the outer cables is 0.08 sq.ins., and the neutral cable is half of this. The current in the positive outer is 150 amps. Calculate the power loss in watts in the cables due to transmission.

77. A shunt generator supplies a full load current of 100 amps., at 110 volts. The stray losses are 500 watts and the shunt field resistance is 55 ohms. If the efficiency at full load is 88%, find the armature resistance, and the input horse power of the generator.

78. A series generator has a series field resistance of 0.3 ohms and an armature of 0.2 ohms. The resistance of the external circuit is 10 ohms and the terminal voltage is 200. Find the electrical horse power output of the generator, and neglecting all other losses than those for the field and armature, find the horse power input to the generator.

79. Describe the system of wiring for the navigation lights of a ship paying particular attention to any automatic indicators which may be fitted. Explain how these indicators work in the event of a navigation light failing?

80. A shunt wound generator supplies 40 amps., at 220 volts. The shunt resistance is 110 ohms and the armature resistance is 0.08 ohms. Find the induced e.m.f. Neglecting other losses than those of the field and armature find the efficiency of the generator.

81. A shunt motor takes 175 amps. The supply voltage is 440. The resistance of the shunt field is 230 ohms and the resistance of the armature is 0.04 ohms. There is a drop of 1.5 volts at the brushes. Find (a) the back e.m.f., of the motor, (b) the horse power, and (c) the efficiency. Consider only the field and armature losses.

82. A 220 volt d.c., motor has a useful torque of 300 lbs.ft. The r.m.p., are 840 and the efficiency at this load is 88%. Find (a) the current taken by the motor, (b) the K.W., hours consumed per day, and (c) the brake horse power of the motor.

83. A shunt generator supplies a shunt motor through cables which have a resistance of 0.3 ohms each. The shunt fields on both motor and generator take 1.5 amps. The resistances of the generator and motor armature are 0.25 and 0.4 ohms respectively. The induced e.m.f., of the generator is 250 volts and a current of 12 amps passes through the motor armature. Find the back e.m.f., of the motor.

84. A shunt motor connected to 115 volt supply main has an armature resistance of 0.02 ohm, a field resistance of 140 ohms, and the back e.m.f., is 109 volts. Calculate;- (a) the armature current (b) the field current and (c) the total current taken by the motor.

85. A d.c., motor has 288 conductors on its armature which is 10 ins., diameter and 8 ins., long. If it develops 15 horse power at 1100 r.m.p., and the field strength is 9,000 lines per sq. cm., and two-thirds of the conductors are effective in producing the torque, find the current flowing in the conductors.

86. The resistances of the armature, field coils and starter of a 220 volt shunt motor are 0.2 ohm, 165 ohms and 9.8 ohms respectively. One end of the field coils is connected to the armature and the other end to the stud of the starter. Make a diagrammatic sketch of the arrangement and calculate, (a) the current through the field coils at the instant of starting; and (b) the total current at the instance of starting; in both of these cases the armature is assumed stationary. Also find the current through the field coils when the motor is running at full load.

87. A motor has 4 poles, its armature is 14 ins., diameter and has 720 conductors whose effective length is 12 ins. The flux density of the field under each pole is 7,000 lines per sq.cm. Each conductor carries 30 amps. If the armature revolves at 680 r.p.m., find the torque in lb.ft., and the horse power developed if only two-thirds of the conductors are effective.

88. A 20 brake horse power shunt wound motor operating from a 200 volt supply has an efficiency of 88%. The armature resistance is 0.1 ohm and the field resistance is 200 ohms. Calculate the total resistance of the starter required to limit the current to 1.5 times the normal full load current at the instant of switching on.

89. For what purpose are interpoles fitted to d.c., generators? By means of a diagrammatic sketch show how the interpoles are arranged and show how the interpole coils and field coils are connected. Mark the polarity of the main and interpoles and indicate the direction of rotation of the armature.

90. Describe the construction of the commutator for a d.c., generator and explain how it functions. State the materials used for the various parts and state what maintenance is required to keep it in good working order.

91. Make a diagrammatic sketch of a series motor fitted with a series diverter. A series motor taking 120 amps from the supply has the series diverter adjusted so that the current through the series field is 90 amps. The resistance of the field is 0.05 ohm. Find the resistance of the series diverter and the power wasted in it.

92. With reference to d.c., generators what is meant by Armature Reaction? Explain what causes this effect and what steps can be taken to eliminate or reduce this effect.

93. What may be causes of the following faults in a d.c., generator;- (a) Sparking at the brushes, (b) Overheating, (c) Failure to excite. In each case state how these causes may be eliminated.

94. With the aid of a sketch describe the construction of a d.c., generator armature and state the materials used for the various parts. Explain the action of the armature.

95. Describe the construction of a compound wound d.c., generator. What is meant by the terms External Characteristics and over compounded?

96. Describe the construction of a d.c., generator suitable for use aboard ship. Make a diagrammatic sketch of the electrical circuit of this type of machine. What normal maintenance does this machine require to keep it in good working condition?

97. A spare armature for a large d.c., motor has been stored for some considerable time. Before bringing the armature into service what inspections and test would be performed on it to be assured that it is in good working condition. Describe how you would perform these tests.

98. Describe the construction of a shunt wound d.c., motor and stae the advantages of this type of machine. How can the speed of a shunt motor be regulated?

99. Some parts of the magnetic circuit of electrical apparatus and machines are laminated. State clearly why this is done and explain what the effect would be if these parts were made from solid metal.

100. What are eddy currents as set up in the parts of a d.c., generator? Explain how these currents are set up and what is done to reduce them. State a type of apparatus in which eddy currents are made use of.

101. Explain carefully how you would conduct a drop test on the armature of a motor in order to detect a open-circuited or broken coil, and also a coil which is short circuiting.

102. A d.c., motor is undergoing overhaul. The brush gear has been removed, and the brushes and commutator are considerably worn. Explain how you would overhaul the commutator to restore it to good working condition, fit new brushes and reposition the brush gear in its correct working position. The machine in question is a large machine fitted with interpoles.

103. Describe the construction of a series wound d.c., motor and state the advantages of this type of machine.. For what purpose can this type of machine be used aboard ship? What is the chief disadvantage of a series motor?

104. With reference to electrical d.c., motors what is meant by the terms Shunt wound, Series wound, and Compound wound. Make a diagrammatic sketch of each showing the electrical circuits in each case and give practical examples of where each type of machine can be used on board ship

105. Describe with the aid of a diagrammatic sketch an electric steering gear.

106. Describe with the aid of a diagrammatic sketch a high-tension magneto ignition system as fitted to a multi-cylinder gasoline engine.