MOD.3 (PART 2.1) - ELECTRICAL FUNDAMENTALS

1) A starter generator has a: low resistance series field and a low resistance shunt field. low resistance series field and a high resistance shunt field. high resistance series field and a low resistance shunt field.

2) If the brake coil on an actuator motor goes open circuit, the actuator will: run slower. stop. over-ride its mechanical stops.

3) If a generator speed is halved and the field strength is doubled, the voltage output will be: unchanged. doubled. halved.

4) How can the direction of rotation of a DC electric motor be changed?. Reverse the electrical connections to either the field or armature windings. Rotate the positive brush one commutator segment. Interchange the wires which connect the motor to the external power source.

5) The only practical method of maintaining a constant voltage output from an aircraft generator under varying conditions of speed and load is to vary the: speed at which the armature rotates. strength of the magnetic field. number of conductors in the armature.

6) Electric motors are often classified according to the method of connecting the field coils and armature Aircraft engine starter motors are generally of which type?. Compound. Shunt (parallel). Series.

7) If a heavy mechanical load is removed from a series motor: the speed will increase and the armature current will increase. the speed will increase and the armature current will decrease. the speed will decrease and the armature current will decrease.

8) If the correct supply were connected to a DC shunt motor which had lost its residual magnetism it would: run in the reverse direction. fail to run. run normally.

9) One purpose of a growler test is to determine the presence of: a shorted armature. a broken field lead. an out-of-round commutator.

10) The purpose of an end-travel microswitch in a linear actuator is to: remain open and closes at end travel only. remain open during normal operation and only close if the actuator overruns its stops. remain closed and opens at end travel only.

11) Linear actuators used in aircraft are of: split field series wound type. compound wound type. split field shunt wound type.

12) If a generator sparks, a possible reason is: the brush springs are loose. magnetic flux deflecting the EMF. the brushes have been placed around the magnetic coil.

13) If the field strength of a generator is doubled, and the speed is doubled, the output EMF will: stay the same. double. quadruple.

14) In a DC motor the pole pairs are: connected to the brush gear. part of the armature. embedded within the field coils.

15) A series wound DC motor, the field has: few turns of thin wire. many turns of thin wire. few turns of thick wire.

16) Doubling the running time of an electrical machine would: double the current used. double the joules used. double the watts used.

17) On a linear actuator, the field cutoff coil will be energized when: only as the actuator commences movement. the actuator is not running. the actuator is running.

18) An electric motor produces a force of 5 N at a distance of 0.2m from the centre of rotation and rotates at a speed of 100 revs/sec. The motors output is: 100 horsepower. 628.4 watts. 314.2 watts.

19) Starter motors are usually: series wound. compound wound. shunt wound.

20) Generator brushes are normally made of: steel. carbon. brass.

21) As the generator load is increased (within its rated capacity), the voltage will: remain constant and the amperage output will decrease. decrease and the amperage output will increase. remain constant and the amperage output will increase.

22) The voltage output of a generator is controlled by: varying the current of the output. varying the resistance of the output. varying the current of the field.

23) The current flowing in the armature of a DC motor is equal to: (applied volts-generated volts) / armature resistance. (applied volts-generated volts) * armature resistance. applied volts + generated volts / armature resistance.

24) What device is used to convert alternating current, which has been induced into the loops of the rotating armature of a DC generator into direct current as it leaves the generator?. An inverter. A commutator. A rectifier.

25) Which of the following is not one of the purposes of interpoles in a generator?. Overcome armature reaction. Reduce arcing at the brushes. Reduce field strength.

26) To reverse the direction of a series motor: the direction of the current through the field and the armature is reversed. the direction of the current through the field is reversed. a second series field is fitted.

27) The current consumed by a DC starter motor will?. remain relatively constant over the starting speed range. decrease as the engine speed increases. increase as the engine speed increases.

28) How are generators rated?. Impedance at rated voltage. Amperes at rated voltage. Watts at rated voltage.

29) Due to armature reaction in a DC motor: the leading pole tips are magnetically weakened. the trailing pole tips are magnetically weakened. the magnetic flux is restored by moving the MNA towards the GNA.

30) Some electric motors have two sets of field winding wound in opposite directions so that the: speed of the motor can be more closely controlled. motor can be operated in either direction. power output of the motor can be more closely controlled.

31) What polarity do interpoles take in a DC motor?. Either, provided they lay on the MNA. The same as the next main pole ahead in the direction of rotation. The same as the next main pole behind in the direction of rotation.

32) What is the principal advantage of the series-wound DC motor?. Suitable for constant speed use. High starting torque. Low starting torque.

33) Interpole windings fitted to DC series wound generators are: in series with the armature. in series with the field. in parallel with the armature.

34) What polarity do interpoles take in a DC generator?. The same as the next main pole behind in the direction of rotation. Either, providing they lay on M.N.A. The same as the next main pole ahead in the direction of rotation.

35) The method most often used in overcoming the effect of armature reaction is through the use of: shaded poles. interpoles. drum-wound armatures in combination with a negatively connected series field.

36) The starting current of a series-wound DC motor, in passing through both the field and armature windings produces a: speed slightly higher when unloaded. high starting torque. low starting torque.

37) To increase the speed of a shunt motor a resistance is placed: in parallel with the field. in series with the field. in series with the armature.

38) A 200 volt motor is taking 10 amperes armature current, the armature resistance is 0.1 ohm. The Back- EMF under these conditions will be: 201 volts. 199 volts. 1 volt.

39) What is a method used for restoring generator field residual magnetism?. Energize the armature. Flash the fields. Reseat the brushes.

40) A high surge of current is required when a DC electric motor is first started. As the speed of the motor increase: the counter emf decreases proportionally. the applied emf increases proportionally. the counter emf builds up and opposes the applied emf, thus reducing the current flow through the armature.

41) Aircraft generators are cooled by: fuel cooling radiators. oil cooling radiators around the main body. ram air.

42) On a combined DC starter - generator system: the voltage regulator is connected to the shunt field after the start cycle is completed. the voltage regulator controls the start sequence during engine starting. the series coil is open circuit during the engine start sequence.

43) If the field current to a shunt wound DC motor is decreased when operating at a constant load, the motor speed will: reduce. not change. increase.

44) ) If a motor is spinning at 50 cycles per second, how long is 1 cycle of the output?. 50 seconds. 0.83 seconds. 0.02 seconds.

45) In a an DC motor, the rotation of the MNA: is opposite to the rotation of the armature. is slightly less speed than the rotation of the armature. is the same as the rotation of the armature.

46) In a wave wound generator with 4 poles, what would be the minimum number of brushes?. 4. 2. 8.

47) A wire is rotated through a magnetic field. To give DC it must be connected to: a commutator. slip rings. a rectifier.

48) If the supply to a DC shunt motor was reversed: it would rotate in the same direction. it would fail to run. it would rotate in the opposite direction.

49) A series motor draws a high current on start, and then the current reduces. This is due to: the resistance of the field and the armature in series. the resistance of the field and armature in parallel. the back EMF.

50) Interpoles in a DC generator are connected: in series with the armature. in series with the field. in parallel with the armature.

51) In a DC generator, the effect of armature reaction may be reduced by moving the brush gear. in the direction of armature rotation towards the MNA. from MNA to GNA. against the direction of armature rotation towards the MNA.

52) The windings embedded in the pole faces of a DC generator are: commutating coils. interpoles. compensating windings.

53) A 6 pole wave-wound generator has: 3 brushes. 2 brushes. 6 brushes.

54) Armature reaction in a DC generator causes: MNA to move in the opposite direction of rotation. MNA to move in the direction of rotation. GNA to move in the direction of rotation.

55) In a DC motor, back-EMF rises if the motor: speed falls. speed faload rises. speed rises.

56) A DC generator armature has 6 poles and is lap wound. The number of brushes required are: 2. 3. 6.

57) Reactive sparking is reduced by: interpoles. compensating windings. auxiliary windings.

58) The back-EMF in a DC motor is: equal to the applied EMF. less than the applied EMF. greater than the applied EMF.

59) The flux density of a magnetic field is 1.5T. The length of the conductor in the field is 2 m and the current flowing through the conductor is 5 amps. The force on the conductor is: 6 Newtons. 15 Newtons. 75 Newtons.

60) A DC shunt motor has 28 volts applied. The current taken from the armature of 2 ohms resistance is 1 amp The Back-EMF is: 26 V. 30 V. 27 V.

61) In a motor, armature reaction causes the MNA to move: against the direction of rotation. in the direction of rotation. to the GNA.

62) In a generator system, a stabilizing winding is used: in series with the field to prevent oscillations. to control output current. to prevent voltage overshoot.

63) What part of a DC motor would you find the poles?. Brushes. Rotor. Stator.

64) An A.C. shunt wound motor sometimes uses a volts dropping resistor. The resistor would be: in series with the field. in series with the supply. in series with the armature.

65) Commutator ripple can be reduced by: increasing generator frequency. the use of a ripple filter. a resistor in series with the armature.

66) In a DC motor the interpoles are part of the: rotor assembly. stator assembly. field.

67) Armature reaction is: the MMF opposing rotation. due to dirty or worn commutator. reactive sparking.

68) A shunt motor: is constant speed. has high starting torque. gives constant torque with variations in speed.

69) In a DC shunt motor, if the field resistance is increased what happens to the back EMF?. Decreases. Remains the same. Increases.

70) To increase the voltage output of a generator you can: decrease speed. It is not speed dependant. increase speed.

71) Generator voltage is: dependant on speed of rotation. independent of speed of rotation. not dependant on speed of rotation.

72) The output from a generator to a commutator is: pulsed DC. DC. AC.

73) What is the main disadvantage of a starter generator?. Heavier than like for like. Will not supply output at low rpm. Can only be used on piston engines.

74) Back-EMF is the greatest when a motor is: at operating speed. under heavy load. just starting to rotate.

75) When a conductor carrying a current and placed in a magnetic field it experiences: an electrostatic force. an electromagnetic force. a magnetic force.

76) The type of motor used in a linear actuator is: parallel (shunt wound). compound. series.

77) If the speed of a coil in a magnetic field is doubled and the field strength is doubled the output will: quadruple. stay the same. halve.

78) How many brushes are used in an 8 pole wave wound machine: 6. 8. 2.

79) In the shunt generator the field is supplied by: the load. the armature. a separate supply.

80) Increasing the speed of an aircraft generator results in an automatic: field circuit resistance decrease. armature circuit resistance increase. field circuit resistance increase.

81) Which generators are usually used on aircraft?. Shunt. Compound. Series.

82) In a cumulative compound wound generator the: the series and shunt fields assist each other. the series and shunt fields oppose each other. the voltage falls suddenly with an increase in load.

83) The shunt wound generator is controlled by a variable resistance in: parallel with the field. series with the armature. series with the field.

84) The series wound generator`s terminal voltage will, when below saturation: increase with an increase in load. decrease with an increase in load. decrease with a decrease in rotational speed.

85) The shunt wound generator is normally started: on load. Either of the above. off load.

86) Armature reaction in a DC motor causes the neutral axis to shift in: the direction in the direction of armature rotation. the direction opposite to the direction of armature rotation. either direction depending on current flow.

87) An indication of good commutation on a DC machine would be: high armature currents. little or no sparking at the commutator. silent operation of the machine.

88) If compound DC generators are operated in parallel they must: all rotate at the same speed. have an equalising or load sharing loop. all use the same voltage.

89) The windings embedded in the pole faces of a generator are: commutating coils. interpoles. compensating coils.

90) Prolonged reactive sparking in a DC generator could damage the: armature. commutator. pole pieces.

91) The poles of a DC generator are laminated to: reduce hysteresis losses. reduce flux losses. reduce eddy current losses.

92) One advantage of a DC motor over an AC motor is: the direction of rotation of the rotor can be changed. less voltage is required in DC than AC. the DC motor will use less current.

93) In a shunt wound direct current motor the torque is: inversely proportional to the current in the armature. independent of load. proportional to the current in the armature.

94) Convention requires that in a symmetrical 3 phase system, the: red voltage is taken as the reference phase. yellow voltage phase leads the red phase by 120 degrees. red voltage phase leads the blue phase by 120 degrees.

95) What is the phase difference in a circuit with 100V, drawing 0.5 amps, consuming 50 Watts?. 0°. 45°. 90°.

96) The power factor of a circuit containing an imbalance of inductive and capacitive reactance is: greater than unity. unity. less than unity.

97) What value is the same as the equivalent D.C. heating effect?. Peak. Average. Root Mean Square.

98) What shape is the waveform when the input pulse and the time base are unequal?. Saw tooth. Square. Rectangular.

99) A sine wave has 5 amps RMS value. What is the peak value?. 7.07 amps. 6.37 amps. 10 amps.

100) What is the wave shape of the x-axis input of a traversing oscilloscope image?. Rectangular. Triangular. Square.

101) In a purely resistive AC circuit, the current vector is: +90° out of phase with the voltage vector. in phase with the voltage vector. -90° out of phase with the voltage vector.

102) When comparing the average values of an AC generator output, to the peak values: average voltage = 0.707 * peak voltage. average voltage = 0.63 * peak voltage. average voltage = same as the peak voltage.

103) A parallel circuit at resonance has: maximum impedance. zero impedance. minimum impedance.

104) A 10 ohm resistor has a 14.14 V peak drop across it. What power is dissipated?. 19.99 W. 10 W. 1.414 W.

105) If a 1 ohm circuit produces a 50 W output, the phase angle is: 45°. 0°. 90°.

106) What does a rectifier do?. Changes alternating current into direct current. Reduces voltage. Changes direct current into alternating current.

107) The ratio between apparent power and true power is the: power rating. power factor. efficiency.

108) Unless otherwise specified, any values given for current or voltage in an AC circuit are assumed to be: effective values. instantaneous values. maximum values.

109) Which aircraft circuit would be most likely to use frequency wild 200V AC?. Hydraulic pump. Windscreen heating. Standby compass.

110) In an AC circuit how is the value of true power calculated?. By voltmeter readings multiplied by ammeter readings. By volts multiplied by amps multiplied by power factor. By watt meter readings multiplied by power factor.

111) One of the chief advantages of alternating current is that it can be transmitted at a high voltage with a low power loss; the voltage can then be changed to any desired value of: DC by means of transformers. DC by means of inverters. AC by means of transformers.

112) How many amperes will a 28-volt generator be required to supply to a circuit containing five lamps in parallel, three of which have a resistance of 6 ohms each and two of which have a resistance of 5 ohms each?. 1 ampere. 25.23 amperes. 1.11 amperes.

113) Frequency (Hz) is the number of cycles per: minute. second. revolution.

114) The frequency of a power wave in an AC resistance circuit is: half the frequency for voltage and current. the same as the frequency for voltage and current. twice the frequency for voltage and current.

115) In an AC circuit, the effective voltage is: less than the maximum instantaneous voltage. equal to the maximum instantaneous voltage. greater than the maximum instantaneous voltage.

116) Which wave form is stepped positive and negative with unequal length sides?. Rectangular wave. Trapezoidal wave. Saw tooth wave.

117) The value of an AC sine wave that will give an equivalent heating effect in a DC resistor is the: peak value. RMS value. average value.

118) The peak factor for a sine wave is: 1.1. 0.707. 1.414.

119) An integrated step input at unequal time base produces: a saw tooth wave. a square wave. a sine wave.

120) A sine wave of RMS value 7.07 volts has a peak to peak value of: 20 volts. 10 volts. 0.707 volts.

121) The true power in an AC circuit is given by: volts * amps. PF * volts * amps. voltmeter reading * PF.

122) The average value of 100 volts peak AC is: 70.7 volts. 141. 4 volts. 63.7 volts.

123) The RMS value of 200 volts peak to peak is: 127.4 volts. 70.7 volts. 141.4 volts.

124) The power factor of an AC circuit is the: cosine of the phase angle. tangent of the phase angle. sine of the phase angle.

125) The Form Factor of an AC waveform can be found by: RMS value divided by the average value. average value divided by the RMS value. average value times the RMS value.