# Electrical Machines MCQ (Interview-Exam) Question-Answer – Principle of Energy Conversion

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## Principle of Energy Conversion

Q.1 What is the coupling field used between the electrical and mechanical systems in energy conversion devices?

A. Electric field

B. None of the mentioned

C. Magnetic field

D. Magnetic field or Electric field

Ans : Magnetic field or Electric field

Q.2 An electro-mechanical energy conversion device is one which converts _______.

A. Mechanical energy to electrical energy only

B. Electrical to mechanical and mechanical to electrical

C. Electrical energy to mechanical energy only

D. None of the above

Ans : Electrical to mechanical and mechanical to electrical

Q.3 The formula for energy stored in the mechanical system of linear motion type is ______.

A. 1/2 mv2

B. Jwr2

C. 1/2 Jwr2

D. 1/2 mv

Ans :  1/2 mv2

Q.4 The energy storing capacity of magnetic field is about ________ times greater than that of electric field.

A. 25,000

B. 40,000

C. 50,000

D. 10,000

Ans : 25,000

Q.5 A coupling magnetic field must react with which of the following statements?
(i) electrical system in order to extract energy from mechanical system
(ii) mechanical system in order to extract energy from mechanical system
(iii) electrical system in order to extract energy from electrical system
(iv) mechanical system in order to extract energy from electrical system
(v) electrical or mechanical system for electro-mechanical energy conversion

A. (ii), (iii) & (v)

B. (ii), (iii) & (v)

C. (i), (ii) & (iii)

D. (ii), (iii) & (iv)

Ans : (ii), (iii) & (v)

Q.6 In an electro-mechanical energy conversion device, which of the following statements are correct regarding the coupling field?
(i) electrical side is associated with emf and current
(ii) electrical side is associated with torque and speed
(iii) mechanical side is associated with emf and current

(iv) mechanical side is associated with torque and speed

A. (ii) & (iii)

B. (i) and (iv)

C. (i) & (ii)

D. (iii) & (iv)

Ans : (i) and (iv)

Q.7 The developed electromagnetic force and/or torque in electromechanical energy conversion systems, acts in a direction that tends to ___________
(i) increase the co-energy at constant flux
(ii) increase the co-energy at constant mmf
(iii) decrease the stored energy at constant mmf
(iv) decrease the stored energy at constant flux
Which of the above statements are correct?.

A. (i), (iii)

B. (i), (iv)

C. (ii), (iv)

D. (ii), (iii)

Ans : (ii), (iv)

Q.8 The developed electromagnetic force and/or torque in electromechanical energy conversion system, acts in such a direction that tends to ___________.

A. decrease the stored energy at constant mmf

B. increase the stored energy at constant flux

C. increase the stored energy at constant mmf

D. decrease the co-energy at constant mmf

Ans : decrease the stored energy at constant mmf

Q.9 A physical system of electromechanical energy conversion, consists of a stationary part creating a magnetic field with electric energy input, and a moving part giving mechanical energy output. If the movable part is kept fixed, the entire electrical energy input will be _______.

A. stored in the electric field

B. zero

C. stored in the magnetic field

D. divided equally between the magnetic and electric fields

Ans : stored in the magnetic field