Questions and Answers on Electric Motor

Feb 8 • Engineering, GATE Syllabus • 53192 Views • 51 Comments on Questions and Answers on Electric Motor

Electric Motor

Electronics in our lives is like the life support which is supporting the human survival and development. They are now the most integrated part of human being. Starting from small toys to large spaceships, small lighting to large space stations, at all places we have the electronics in various forms with us. Let it be concentrated over the Electric Motors. Electric Motors are the machines that convert electrical energy into the mechanical energy which further is used to drive a vehicle, plant and many more things around us. Here are the types of questions on electric motors which are asked in an interview, question papers and other competitive exams as well.

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Questions on Electric Motors with answers-

Q1. WHAT IS ELECTRIC MOTORS?
ANS. An electric motor is an electrochemical device that converts electrical energy into mechanical energy. Most electric motors operate through the interaction of magnetic field and current carrying conductors to generate force.

Principle of working of Electric Motor

Principle of working of Electric Motor

Q2. ON WHAT PRINCIPLE ELECTRIC MOTOR WORKS?
ANS. The Motor Principle: when a current-carrying conductor is located in an external magnetic field perpendicular to the conductor, the conductor experiences a force perpendicular to itself and to the external magnetic field.The physical principle behind production of mechanical force by the interactions of an electric current and a magnetic field.

The right-hand rule for force on a conductor can be used to determine the direction of the force experienced on the conductor.

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Q3. HOW MANY TYPES OF ELECTRIC MOTORS ARE THERE?
ANS. Mainly there are two types of electric motors:
a. AC motors
b. DC motors

Q4. WHAT IS AC MOTOR?
ANS. An AC motor is an electric motor driven by an alternating current (AC). It commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field.

Group Discussion

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Q5. WHAT IS DC MOTORS?
ANS. A DC motor is a mechanically commutated electric motor  powered from direct current (DC). The stator is stationary in space by definition and therefore so is its current. The current in the rotor is switched by the commutator to also be stationary in space. This is how the relative angle between the stator and rotor magnetic flux is maintained near 90 degrees, which generates the maximum torque.

Q6. WHAT ARE THE APPLICATIONS OF ELECTRIC MOTOR?
ANS. Electric motors applications are: industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives, record players.

Q7. WHAT ARE THE ADVANTAGES AND DISADVANTAGES OF AC, DC MOTORS?
ANS. Advantages of AC Motors:
Low cost,
long life,
high efficiency,
large ratings available (to 1 MW or more),
large number of standardized types.

Disadvantages of AC Motors:
Starting inrush current can be high,
speed control requires variable frequency source.

Advantages of DC Motors:
Precision positioning,
High holding torque,
Long lifespan,
Low maintenance,
High efficiency

Disadvantages of DC Motors:
Some can be costly,
Require a controller,
Higher initial cost,
Requires a controller.

Universal Motors

Universal Motors

Q8. WHAT IS UNIVERSAL MOTOR?
ANS. A series-wound motor is known as a universal motor when it has been designed to operate on either AC or DC power. It operate well on AC because the current in both the field and the armature (and hence the resultant magnetic fields) will alternate in synchronism and hence, the resulting mechanical force will occur in a constant direction of rotation.

Q9. HOW IS THE EFFICIENCY OF MOTOR IS CALCULATED?
ANS. To calculate a motor’s efficiency, the mechanical output power is divided by the electrical input power: \eta = \frac{P_m}{P_e}, where \eta is energy conversion efficiency , P_e is electrical input power, and P_m is mechanical output power.

In simplest case P_e = V I, and P_m = T \omega, where V is input voltage, I is input current, T is output torque, and \omega is output angular velocity. It is possible to derive analytically the point of maximum efficiency. It is typically at less than 1/2 the stall torque.

Q10. WHAT ARE THE STANDARDS OF MOTOR?
ANS. The following are major designs and manufacturing standards covering electric motors:

  • International Electro-technical Commission: IEC 60034 Rotating Electrical Machines
  • National Electrical Manufacturers Association (USA): NEMA MG 1 Motors and Generators
  • Underwriters Laboratories (USA): UL 1004 – Standard for Electric Motors

Download the questions on electric motor with their answers at QUESTIONS ON ELECTRIC MOTOR WITH ANSWERS PDF

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51 Responses to Questions and Answers on Electric Motor

  1. rheal says:

    when dismantling electric motor do you punch mark the de bell end with two marks or one

  2. satendra singh says:

    Enter your any educational query or doubt -electrical engineer

  3. Anant Grewal says:

    To pass the exam of asynchronous machines.

  4. Hitesh says:

    What is the frame size of a motor ? Explain in derails with given the example of motor.

  5. Hitesh says:

    What is the frame size of a motor ? Explain in derails with given the example of motor.

  6. Ali Ahsan says:

    I am doing electrical engineering from UOG 1st semester.

  7. Ali Ahsan says:
  8. NS Rahim says:

    ELECTRICAL ENGINEERING

  9. Manoj Kumar verma says:

    polytechnic

  10. Gajawada Prajwal says:
  11. vikram says:

    b tech inEE

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  23. Anonymous says:
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  26. fawad yousaf says:

    dae elect

  27. Gajendra says:

    About electric vehicle

  28. Anonymous says:
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  30. moses obanyedo says:

    diploma in electrical and electronics

  31. pritam kumar says:

    iti electral grejuation

  32. Anonymous says:
  33. Emmanuel Muzanenhamo says:

    engineering

  34. Emmanuel Muzanenhamo says:

    engineering

  35. Emmanuel Muzanenhamo says:

    engineering

  36. Emmanuel Muzanenhamo says:

    engineering

  37. Emmanuel Muzanenhamo says:

    engineering

  38. araya says:

    interview questions and answers about electrical machines

  39. Sonu Bairwa says:

    I want to learn the power system, machine and other topics related to interviews…

  40. Ayomide Emmanuel Gbadebo says:

    I need questions and solutions related to mechanical engineering

  41. cyprien ndindiyaho says:

    questions and answers about starting electrical motor

  42. Elifas Ndangi Shimana says:

    I want to help my Grade 10 learners on Electric motor :(a) how does it work ? How does it produce electricity?
    How does it generate electricity?. and How can I connect it .

  43. Joseph Galese says:

    Outside compressor fan for the AC is spec’d for .5 amps, but it’s reading .57 amp draw with extensive use; does this motor have to be replaced?

  44. Ch.S.Balasubrahmanyam says:

    When Induction Motor is fed from Rotor side then what is the frequency of Stator ?

  45. abhimanyu singh says:

    after completing my i.t.i in electrical in 2009,i’m working in this field from last 5-5.5 years,now i want to do diploma in same field,can u plz suggest me any college or intitute having aicte approval for diploma in distance mode.

  46. parthiban says:

    i am stdying for eee.very confusion for goto way jobs.plz say ur tips

  47. Gowtham says:

    any one send a interview questions about drives and sensors

  48. Jaimim Gohil says:

    I have need to sport to creaking interview?

    how to possible that?

  49. DINESH KUMAR says:

    what is the basic function of capacitor for leading current, and how it improve power factor.

  50. mahesh sanjay navaghane says:

    why induction motor called as constant speed motor?

  51. huma fatima says:

    this topic is from mechanical trade….we all are using this device daily..It takes great effort to learn them.

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