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DC Motors Questions

Resolved Question:

DC Motors Questions (SEE POST BELOW (dated 2/2/2013) FOR NEW QUESTIONS THAT NEED TO BE ANSWERED)


 


Do NOT answer these questions in this box:


1. Flexible cord as a form of electrical conductor shall not Customer Question Ask your own question now > 1. Flexible cord as a form of electrical conductor shall not be used A. as a connection for ranges and clothes dryers. B. as a substitute for fixed wiring. C. for connecting portable equipment. D. for wiring cranes and hoists. 2. If a three-phase four-wire AC circuit uses colour coded conductors, the colour of the phase C should be A. black. C. blue. B. white. D. red. 3. A 16-kW residential electric range shall be considered to have a branch circuit demand of A. 8 kW. C. 16 kW. B. 9.6 kW. D. 17.6 kW 4. What minimum size of copper wire should be used to connect between a lightening arrester and a line conductor? A. No. 2 AWG C. No. 6 AWG B. No. 4 AWG D. This connection is not permitted. 5. In an indoor station containing a high-voltage installation, the station grounding system must be connected to the main ground electrode with a minimum of A. one No. 4 AWG conductor. C. one No. 2/0 AWG conductor. B. two No. 4 AWG conductors. D. two No. 2/0 AWG conductors. 6. In a residential bathroom there should be a distance of at least ________ between a bathtub and a receptacle. A. 0.75 m C. 1.2 m B. 1 m D. 1.8 m 7. When communications conductors pass over a building with a flat roof, the minimum clearance between the conductor and the roof shall be A. 1 m. C. 3 m. B. 2.5 m. D. 4.5 m. 8. The presence of which one of the following materials makes an area a Class II hazardous location? A. Flammable gases C. Easily ignitable fibres B. Combustible flyings D. Combustible dust 9. A capacitor rated at 1000 volts should have a means of reducing the residual voltage to A. 50 V within 5 min. C. 50 V within 1 min. B. 100 V within 5 min. D. 100 V within 1 min. 10. The largest current capacity permitted for standard cartridge fuses is A. 30 A. C. 600 A. B. 250 A. D. 1000 A. 11. The minimum size of copper conductors that can be used for the control and signal wiring for traveling cables in elevators, is A. No. 20 AWG. C. No. 16 AWG. B. No. 18 AWG. D. No. 12 AWG. 12. The maximum number of No. 10 AWG conductors permitted in a 4 × 21 /8-in. square box is A. 13. C. 10. B. 12. D. 8 13. A class III hazardous location would contain A. readily ignitable fibres C. electrically conductive gases. B. flammable, volatile liquids. D. unguarded machinery. 14. An automatic resistance welder has an actual primary current of 30 amperes. If the welder operates with a duty cycle of 40%, the supply conductors shall have an ampacity of not less than A. 12 A. C. 18.9 A. B. 15.75 A. D. 30 A. 15. One requirement for use of incandescent lamps as protective resistors is that the lamps A. shall carry or control the main current. B. shall constitute the regulating resistance for the device. C. shall be selected so that the impressed voltage does not exceed the lamp rating. D. shall be mounted in a metal receptacle on supports to prevent possible ignition in case of an overload. 16. An electric storage tank water heater whose tank is not open to the atmosphere must be equipped with a device to A. reduce voltage. C. filter and maintain water purity. B. sense the maximum current. D. limit temperature. 17. In underground service installations where the conductors are directly buried, and must have a maximum allowable conductor temperature of 75°C, it is permissible to use A. electrical metallic tubing. B. nonmetallic sheathed cable. C. intermediate metallic conduit. D. aluminum-sheathed type RA75 cable. 18. The maximum number of No. 6 AWG 600-V thermoplastic insulated conductors that may be placed in a 2-in. conduit is A. 6 C. 18 B. 9 D. 20 19. If the bare main contact conductors for a hoist are 21 m long and do not have intermediate supports, the smallest copper wire that may be used for the conductors is A. No. 2 AWG. C. No. 6 AWG. B. No. 4 AWG. D. No. 8 AWG 20. Surface raceways can be installed for use where A. #8 AWG aluminum conductors are used. B. the voltages between the conductors will not exceed 500V. C. fixtures require support. D. they are concealed from view. 21. Overcurrent trip coils used as motor overload protection for a three-phase AC motor on a three-phase four-wire AC system should be installed with A. one trip coil in the neutral conductor. B. three trip coils, one in each ungrounded conductor. C. two trip coils, one in any two ungrounded conductors. D. two trip coils, one in the neutral conductor and one in an ungrounded conductor. 22. The proper operation of emergency systems must be ensured by testing at least once every A. day.

Submitted: 1 year ago.
Category: Homework
Expert:  Josie-Mod replied 1 year ago.

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I wonder whether you're ok with continuing to wait for an answer. If you are, please let me know and I will continue my search. If not, feel free to let me know and I will cancel this question for you. Thank you!

Customer: replied 1 year ago.

hi


i a m waiting for your answer, i believe this question have been answered before


 


thank you


best regards

Expert:  Josie-Mod replied 1 year ago.
Thank you for your continued patience. We will continue the search for a Professional for you.
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Expert:  Seanna replied 1 year ago.
Hello. It looks like your exam was cut off- the text stops with A. on #22. Also, depending upon how many questions, would you consider increasing the value? Finally, what text are you using?
Customer: replied 1 year ago.

please answer me

Customer: replied 1 year ago.

no problem seanna i will appreciated if you answer me the questions till 21


 


thank you

Expert:  Seanna replied 1 year ago.
Hi, I would still need the textbook information, I will opt out in case another Professional can answer without it. Best,

Seanna
Expert:  Josie-Mod replied 1 year ago.
Hi, I’m a Moderator for this topic. It seems the Professional has left this conversation. This happens occasionally, and it's usually because the Professional thinks that someone else might be a better match for your question. I've been working hard to find a new Professional to assist you right away, but sometimes finding the right Professional can take a little longer than expected.

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Customer: replied 1 year ago.
I am waiting
Expert:  Josie-Mod replied 1 year ago.
Thank you for your continued patience. We will continue the search for a Professional for you.
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Customer: replied 1 year ago.

still waiting

Expert:  Josie-Mod replied 1 year ago.
Thank you for your reply. Your question is open to all the Professionals and marked high priority. You'll receive an email notification if a Professional replies. We appreciate your patience.
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Thank you for your patience, your business is very important to us, we are waiting on the Professional with the right expertise to come online. Feel free to let us know if you would like us to continue searching for a Professional or if you would like us to close your question. Thank you for your understanding!
Customer: replied 1 year ago.

still waiting.

Customer: replied 1 year ago.

too late: please answer me the below instead:


1. Which of the following DC motors provides the highest starting torque?
A. Series-wound C. Compound-wound
B. Shunt-wound D. Generator-wound
2. What is the efficiency of a DC generator that requires 100 watts of energy to supply 80 watts of output
power?
A. 8% C. 80%
B. 12.5% D. 125%
3. Which of the following DC motors acts as a form of electrical ratchet?
A. Servo C. Stepper
B. Permanent-magnet D. Syncro
4. Why is steel alloyed with silicon used as the core material for the armature of a DC generator?
A. To reduce eddy-current flow in the armature core
B. To increase the hysteresis loss in the core
C. To decrease the resistance of the armature conductors
D. To reduce the resistance to current flow in the core
5. Which of the following losses can happen even when a DC generator isn’t connected to a load?
A. I2R loss C. Copper loss
B. Brush friction loss D. Iron loss
6. If a DC generator with an efficiency of 94% has an output of 240 volts at 100 amperes, the machine
power losses for this generator would be
A. 1175 watts. C. 1532 watts.
B. 1487 watts. D. 1655 watts.
7. What happens when the speed of a generator’s armature increases?
A. The load decreases C. The windage loss decreases
B. The field current reverses D. The induced voltage increases
8. To get better commutation in a DC generator, you should move the brushes
A. in the direction of rotation.
B. in the direction of field polarity.
C. against the direction of rotation.
D. against the direction of field strength.
9. Which of the following DC motor drive systems controls motor speed by controlling the period of the
waveform to the drive’s output transistor?
A. Frequency-effect transition (FET)
B. Frequency-drift commutation (FDC)
C. Pulse-controlled modulation (PCM)
D. Pulse-width modulation (PWM)
10. In a generator, the voltage induced in a rotating armature coil is at maximum when the coil
A. moves parallel with the magnetic lines of force.
B. cuts the fewest magnetic lines of force.
C. is at right angles to the magnetic lines of force.
D. is in a vertical position between the field poles.
11. Which of the following methods can be used to cut down on brush sparking in a DC generator?
A. Install interpoles in the armature core.
B. Install compensating coils in the field pole faces.
C. Move the brushes against the armature rotation.
D. Connect commutating coils in parallel with the armature coils.
12. Technician A is told to inspect and clean the brush holders and replace the brushes in a DC generator.
Which of the following areas would the technician be working on in this case?
A. The base C. The rigging
B. The commutator D. The shaft
13. Which of the following devices did older DC motor speed controllers often use to control armature
voltage?
A. A battery C. A potentiometer
B. A rheostat D. A diode
14. What is the efficiency of a DC generator that requires 200 watts of energy to supply 160 watts of
output power?
A. 40% C. 90%
B. 80 % D. 125%
15. In a field weakening DC motor speed controller system, what happens when the voltage to the field is
decreased?
A. The motor speed will increase.
B. The motor will slow down.
C. Sparking will occur at the commutator.
D. Excess heat will be generated.
23. Which of the following types of motors is usually used in machine tools and precision positioning
equipment?
A. A series-wound DC motor
B. A DC permanent magnet servo motor
C. A compound-wound DC motor
D. A shunt-wound DC motor
24. If the current in a generator’s armature increases from two amps to eight amps, what is the increase
in copper losses?
A. Four times C. Six times
B. Sixteen times D. Thirty-six times
25. What is the efficiency of a generator that produces 80 kilowatts of electric energy and has electric and
mechanical losses of 20 kilowatts?
A. 58.3% C. 60%
B. 80% D. 100%

Expert:  Josie-Mod replied 1 year ago.
Thank you for your reply. Your question is open to all the Professionals and marked high priority. You'll receive an email notification if a Professional replies. We appreciate your patience.
Expert:  Josie-Mod replied 1 year ago.
Thank you for your patience, your business is very important to us, we are waiting on the Professional with the right expertise to come online. Feel free to let us know if you would like us to continue searching for a Professional or if you would like us to close your question. Thank you for your understanding!
Customer: replied 1 year ago.

Surprised

Expert:  Chris M. replied 1 year ago.
Hello, and thanks for the question.

Here are the answers for comparison with your own. Note: Questions #!6-22 were not posted. If you need assistance with those questions, please let me know.

1. A. Series-wound
2. C. 80%
3. C. Stepper
4. A. To reduce eddy-current flow in the armature core
5. B. Brush friction loss
6. C. 1532 watts.
7. D. The induced voltage increases
8. C. against the direction of rotation.
9. D. Pulse-width modulation (PWM)
10. C. is at right angles to the magnetic lines of force.
11. A. Install interpoles in the armature core.
12. B. The commutator
13. B. A rheostat
14. B. 80 %
15. A. The motor speed will increase.
23. A. A series-wound DC motor
24. B. Sixteen times
25. B. 80%

Hope this helps!
Chris M., M.S.W. Social Work
Category: Homework
Satisfied Customers: 2479
Experience: Master's Degree, strong math and writing skills, experience in one-on-one tutoring (college English)
Chris M. and 11 other Homework Specialists are ready to help you
Customer: replied 1 year ago.


























































































































































































Question NumberYour AnswerAnswerReference





1.ACorrect
2.CCorrect
3.CCorrect
4.ACorrect
5.BCorrect
6.CCorrect
7.DCorrect
8.ACorrect
9.DCorrect
10.CCorrect
11.CBPAGES 38-39
12.BCPAGE 26
13.BCorrect
14.BCorrect
15.ACorrect
16.CCorrect
17.CCorrect
18.DCorrect
19.DCorrect
20.DCPAGE 17
21.BCorrect
22.ACorrect
23.BCorrect
24.BCorrect
25.BCorrect
Customer: replied 1 year ago.

dear


it was too late for last answers, now can you help with this please


 


 


1. When you’re taking a PM motor apart you should exercise special care not to damage the
A. end bells. C. permanent magnets.
B. commutator. D. brush holders.
2. Which one of the following motor types uses permanent magnets in the armature or rotor?
A. Stepper motor C. PM servo motor
B. PM motor D. Pancake motor
3. The magnetic material that’s placed inside a coil of wire in a motor is called a
A. pole. C. form.
B. concentrator. D. rod.
4. As you walk up to a machine, you see a technician tapping on the back section of a DC motor with a lead mallet.
This technician is
A. cleaning the commutator. C. checking for end bell cracks.
B. looking for weak or worn brushes. D. reseating the rear end bell on the case


5. What type of motor has the same wire diameter in both the field and the armature coils?
A. Series-wound C. Shunt-wound
B. Interpole-wound D. Compound-wound
6. The large current that a DC motor will draw on start-up is called
A. velocity current. C. inrush current.
B. dynamic current. D. acting current.
7. The opposition to the flow of magnetic flux is called
A. resistance. C. reluctance.
B. friction. D. magnomotive force.
8. A DC motor that has interpoles will have the interpole windings in
A. series with the field windings. C. series with the armature.
B. parallel with the field windings. D. parallel with the armature.
9. If the field windings of a 50/100 VDC motor are connected to a 100 VDC source of power, the field windings
should be connected in
A. series with each other. C. series with the armature.
B. parallel with each other. D. parallel with the armature.
10. The energy that’s lost in a DC motor is rather small. Most of the energy is lost as
A. stray magnetic fields. C. windage losses inside the motor.
B. friction in the bearings. D. heat losses to the case.
11. There are two wires labeled P1 and P2 at a DC motor’s junction box. These wires will attach to what internal
component of the motor?
A. Ground C. The parallel winding
B. A thermostat D. A speed potentiometer
12. The letters CEMF are used to describe
A. centrifugal forces within a motor.
B. countervoltages and currents created within a motor.
C. critical winding currents that should not be exceeded.
D. the portion of the supplied current that is converted to heat.
13. The major failure area of a typical wound-field and wound-armature DC motor is
A. open field windings. C. bearing failure.
B. brush wear and failure. D. a faulty commutator segment.
14. A normal commutator will have which one of the following colors where the brushes contact the commutator?
A. Black C. Slate-gray
B. Chocolate-brown D. Auburn-brown
15. A PM field servo motor may be equipped with a resolver that is used to
A. excite the armature windings. C. feed back position information.
B. prevent the brushes from sparking. D. create a voltage that increases with velocity.


16. One common type of electronic circuit component that is used to control the voltage and current to a DC motor
is the
A. resistor. C. diode.
B. silicon-controlled rectifier. D. capacitor.
17. An encoder is a device that is used to
A. commutate the field windings. C. reduce brush sparking.
B. feed back position information. D. excite the motor’s interpoles.
18. When field voltage is controlled to provide a method of variable speed control, the system is using a concept
known as field
A. weakening. C. stability.
B. bias. D. drive.
19. If an electronic control system is starting a motor, it will keep start-up current within limits by using
A. a rheostat and a relay. C. an acceleration ramp.
B. a pulsed diode control. D. coast-up system.
20. Which one of the following types of motors can be powered with either AC or DC electricity?
A. Shunt-wound motor C. Universal motor
B. Servo motor D. Pancake motor
21. The magnets that are used in the field of a quality DC PM motor are made from
A. rare-earth material. C. natural magnets.
B. magnetized steel. D. special aluminum-nickel compounds.
22. Which one of the following types of motors is not normally reversible?
A. Servo motor C. Universal motor
B. PM motor D. Brushless DC motor
23. A type of resistance device that can be placed in a DC motor circuit and varied to limit the speed of a motor is
called a
A. potentiometer. C. power resistor.
B. variable reluctor. D. rheostat.
24. The stray currents that are created as a magnetic material is magnetized and then demagnetized are called
A. pole currents. C. hysterysis currents.
B. eddy currents. D. lag currents.
25. The metal plates that are riveted or bolted together inside a motor are called
A. cores. C. sheaves.
B. discs. D. laminations.

Expert:  Chris M. replied 1 year ago.
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