Description : The amount of mechanical force or torque produced by an electric motor depends on the ________________. A. strength of its magnetic field B. amount of armature current flow C. length of conductor in the field D. all of the above
Last Answer : Answer: D
Description : A single-phase induction motor having a relatively high starting torque, is the ___________. A. shaded pole motor B. wound-rotor motor C. capacitor-start motor D. resistance-start motor
Last Answer : Answer: C
Description : Which of the listed electrical devices is represented by the symbol shown in the illustration? EL-0055 A. Fixed resistance resistor B. Coil with magnetic core C. DC motor or generator shunt field D. Transformer
Description : A galvanometer is an instrument used to measure ___________. A. thickness of galvanized metal B. resistance of electrical wiring insulation C. very small amounts of current or voltage D. quantity of galvans in an electric circuit
Description : The d.c. series motor should always be started with load because (A) at no load, it will rotate at dangerously high speed. (B) it will fail to start. (C) it will not develop high starting torque. (D) all are true.
Last Answer : (A) at no load, it will rotate at dangerously high speed.
Description : The electrical diagram shown in the illustration shows _____________. EL-0021 A. 'R1', 'R2', and 'R3' are connected is series B. 'R1', 'R2', and 'R3' are connected in parallel C. the voltages measured across ... if 'R1', 'R2' and 'R3' have different values D. the total resistance equals R1 + R2 + R3
Last Answer : Answer: B
Description : As compared to shunt and compound DC motors, the series DC motor will have the highest torque because of its comparatively ____________ at the start. (A) Lower armature resistance. (B) Stronger series field. (C) Fewer series turns. (D) Larger armature current.
Last Answer : (D) Larger armature current.
Description : AC and DC generators are similar in that they _____________. A. both generate alternating voltages B. both rectify the voltage before delivery C. are constructed at the same physical size for the same kilowatt rating D. both supply three-phase power
Last Answer : Answer: A
Description : The illustrated circuits are used to measure ___________. EL-0024 A. resistance B. gauss or magnetic field strength C. battery discharge rate in Amp-hours D. current
Description : Electric propulsion coupling excitation is reduced at slow speeds to ___________. A. increase speed control B. increase shaft torque C. prevent coupling overheating D. prevent coupling slippage
Description : A synchronous motor starts as usual but fails to develop its full torque. What could it be due to?
Last Answer : a. Exciter voltage may be too low. b. Field spool may be reversed c. There may be either open-circuit or short-circuit in the field.
Description : Basic electrical motor action depends on _______________. A. a conductor rotated within a magnetic field B. a current carrying conductor placed in a magnetic field C. the relative force of the commutator and commutating poles D. the relative force of the armature and interpoles
Description : A transformer in an electric circuit serves to ____________. A. generate its own electrical power B. transform electrical energy into mechanical energy C. increase or decrease circuit voltage as required D. convert AC current to DC current
Description : A characteristic of a wound-rotor induction motor, with a high resistance rotor winding, is _____________. A. low starting torque B. high starting torque C. high speed D. low starting voltage
Description : A double squirrel-cage motor is designed to have __________. A. low starting torque B. low starting current C. high starting voltage D. low starting resistance
Description : Why is the starting torque of a resistance split-phase induction motor not high?
Last Answer : The starting torque is given as, Ts = K Im Is Sin Ф Where K = constant whose magnitude depends upon the design of the motor (i) The angle between Is and Im is small ... Im are not equal in magnitude, the rotating magnetic field is not uniform and the starting torque produced is small.
Description : How can a magnetic field be used to generate an electric current?
Last Answer : Magnetic field can be used to generate electric current on a condition that it is on a rate of changing magnetic flux. (Faraday's law)
Description : At high discharge rates, nickel-cadmium storage batteries are superior to lead-acid batteries because they __________. A. require fewer cells for the same voltage and less mounting space B. are able to ... times without much damage D. have no individual cells to replace at the end of useful life
Description : Which of the following precautions should be taken when troubleshooting various power circuits using a common solenoid-type mechanical voltage tester (wiggins)? A. Never use this tester on circuits greater ... voltage expected in the circuit in order to prevent damage from an off-scale reading.
Description : The rotor slots of a repulsion-type motor are generally skewed (placed nonparallel to the rotor axis) to _________. A. produce a constant starting torque B. permit a greater air gap with the starter C. permit a smaller air gap with the starter D. reduce eddy current losses
Description : In a 15 HP induction-type motor with a cage rotor, the current required at standstill to produce starting torque is approximately ____________. A. half the full load current B. equal to the full load current C. five times the full load current D. ten to twenty times the full load current
Description : Which of the following statements describes what will occur if the motor shown in the illustration is required to carry 150% of full load? EL-0056 A. The primary counter emf will be increased. B. ... slip will decrease. D. The slip value, stator current curve, and torque curve will all coincide.
Description : The electrical diagram shown in the illustration represents a ___________. EL-0054 A. series-wound motor B. shunt-wound motor C. compound-wound motor D. flat-compounded motor
Description : As part of a routine maintenance program for deck machinery, you should ___________. A. inspect electrical wiring and pushbutton switches for evidence of corrosion or burned insulation B. disassemble ... covers and ventilate as weather permits D. Check drum switch contact pressure every three months
Description : The air gap in an induction motor should be periodically checked with a feeler gage to prevent possible ___________. A. rotor contact with the stator B. axial misalignment of the rotor C. damage to the motor bearings D. electrical damage to the bearings
Description : The full load torque of an electric motor is the __________. A. minimum torque developed by the motor accelerating from stop to full speed B. turning moment exerted by the motor at rated load ... and frequency D. turning moment exerted by the motor from any rotor angular position at any load
Description : Due to its construction, the component in figure 'A' shown in the illustration has which of the listed advantages compared to bipolar devices? EL-0078 A. Operates with higher voltages and ... as a controllable rectifier. D. Has very high input resistance and uses practically no gate current.
Description : Moisture accumulating in electric motors and generator windings having a cold insulation resistance greater than 50,000 ohms may be baked out with internal heat. This heat can be developed by ____________. ... an electric welder and feeding it into the armature while running the motor at full speed
Description : Regarding an induction motor, the power developed by the rotor automatically adjusts itself to the _____________. A. power required to drive the load B. speed required to drive the load C. current flow in the motor stator D. torque developed by the rotating field
Description : The purpose of a cage rotor winding placed on the rotor of a synchronous motor is to _____________. A. provide excitation to the DC field B. start the machine as an induction motor C. contribute extra torque at synchronous speed D. prevent the machine from falling out of step
Description : A dc cumulatively compounded motor delivers rated load torque at rated speed. If series field is short circuited, then the armature current and speed will a) Both increases b) Both decreases c) Increases and decreases d) Decreases and increases
Last Answer : Ans: Both increases
Description : The purpose of a magnetic relay is to _____________. A. open a circuit only in the event of overload B. remotely open and close contacts C. provide overcurrent protection during starting D. relay voltages at increased power
Description : What is the main function in the use of a capacitor for starting a single phase motor? A. Reduce radio interference B. Split the phase to establish a rotating magnetic field C. Reduce the phase angle D. Prolong the life of the starting contacts
Description : The function of the commutator in a DC motor is to ________. A. reverse the flow of current through the armature B. reverse the flow of current in the field poles C. reduce the reluctance of the magnetic path through the motor D. shift the neutral running plane of the brushes to prevent sparking
Description : Some large A.C. motors are equipped with with heaters. These could be ___________. I. resistance heaters bolted directly to the frame II. low voltage windings embedded in the motor windings A. I only B. II only C. either I or II D. neither I or II
Description : Which of the following statements is correct for the illustrated circuit? EL-0020 A. 'R1', 'R2', and 'R3' are connected in series. B. 'R1', 'R2', and 'R3' are connected in parallel. C. The voltages measured across 'R1', 'R2', and 'R3' are equal. D. The total resistance equals 1/R1 + 1/R2 + 1/R
Description : Which of the following statements is true concerning simple parallel resistance circuits? A. The total current flow equals the sum of the individual currents. B. The total current flow equals the ... resistance. D. The total voltage equals the sum of the individual voltages across each resistance.
Description : Which of the following statements concerning a simple parallel resistance circuit is correct? A. The voltage drop across each resistor is the same. B. The total current flow equals the reciprocal ... resistances. D. The total voltage equals the sum of the individual voltages across each resistance.
Description : The function of amortisseur, or damper windings in a synchronous motor is to _____________. A. eliminate slippage B. provide excitation C. provide starting torque D. increase efficiency
Description : The function of damper windings in a synchronous motor is to _____________. A. eliminate slippage B. provide excitation C. provide starting torque D. increase efficiency
Description : A d.c. motor develops a torque of 200 N-m at 25 rps. At 20 rps it will develop a torque of .......... N-m.
Last Answer : A d.c. motor develops a torque of 200 N-m at 25 rps. At 20 rps it will develop a torque of 200 N-m.
Last Answer : A synchronous motor can develop synchronous torque at synchronous speed.
Description : The air gap in an induction motor should be checked periodically with a feeler gage to detect ____________. A. rotor contact with the laminations B. changes in armature magnetic strength C. excessive bearing wear D. electrical damage to the rotor
Description : What is the function of the interpoles installed in DC motors? A. To provide greater torque by strengthening the main field. B. To provide sparkless commutation without having to shift the brushes. C. To limit the production of counter-electromotive force. D. To limit the starting surge current.
Description : Which of the following statements is true concerning the cleaning of electrical contacts? A. Compressed air should be used to blow out metallic dust. B. Magnetic brushes should be used to remove ... contact resistance. D. Delicate parts should be cleaned with a brush and an approved safety solvent.
Description : An electric current can produce a) heating effect c)chemical effect b) magnetic effect d)chemical, magnetic and heating effect
Last Answer : d)chemical, magnetic and heating effect
Description : To minimize magnetic field interaction between electrical conductors in physical proximity, it is best to keep them ___________________. A. parallel and as close as possible to each other B. at right angles ... practicable from each other D. at right angles and as far as practicable from each other
Description : An electrical device which employs a stationary armature and a rotating electromagnetic field is used aboard ship as a ____________. A. magnetic amplifier B. ship's service alternator C. three-wire DC generator D. saturable core reactor
Description : A fuse will 'blow' if _____________. A. an electric motor is stopped suddenly by opening a switch B. the flow of current to the protection device is reversed C. the electrical current exceeds the rated value of the fuse D. unequal resistors are connected in parallel
Description : An electrical connection between the wiring of an electric motor and its metal frame is known as a/an _____________. A. eddy current B. ground C. impedance D. flux leakage