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1.	Electromagnetic force and/or torque developed in any physical system, acts in such a direction as to tend to ____________(a) increase both the field energy and co-energy at constant current(b) increase the field energy and decrease the co-energy at constant current(c) decrease both the field energy and co-energy at constant current(d) decrease the field energy and increase the co-energy at constant currentThis question was addressed to me in quiz.The question is from Singly Excited Magnetic Systems topic in portion Magnetic Circuits of Electrical Machines
Answer» CORRECT choice is (a) increase both the FIELD energy and co-energy at CONSTANT current To elaborate: fe = (∂Wfld^1(i,x))/∂x = (∂Wfld(i,x))/∂x.

2.	The electromagnetic torque developed in any physical system, and with magnetic saturation neglected, acts insuch a direction as to tend to ____________(a) decrease both the reluctance and inductance(b) increase both the reluctance and inductance(c) decrease the reluctance and increase the inductance(d) increase the reluctance and decrease the inductanceThis question was addressed to me in a job interview.This key question is from Singly Excited Magnetic Systems topic in section Magnetic Circuits of Electrical Machines
Answer» Right CHOICE is (C) decrease the reluctance and INCREASE the inductance Explanation: fe=1/2 ∅^2dRl/dx, Te=-1/2 ∅^2dRl/dθ = 1/2 i^2dL/dθ.

3.	Consider a magnetic relay with linear magnetization curve in both of its open and closed position. What happens to the electrical energy input to the relay, when the armature moves slowly from open position to closed position?(a) Welec=Wfld(b) Welec=Wmech(c) Welec=Wmech/2+Wfld/2(d) Welec=0This question was addressed to me in semester exam.Query is from Singly Excited Magnetic Systems in chapter Magnetic Circuits of Electrical Machines
Answer» Correct choice is (C) Welec=Wmech/2+Wfld/2 To explain I would SAY: For the above mentioned case, Wfld=Wmech and Wfld=Welec/2 HENCE, OPTION “c” is the correct answer.

4.	The electromagnetic force developed in any physical system acts in such a direction as to tend to _____________(a) decrease the co-energy at constant mmf(b) increase the co-energy at constant flux(c) decrease the co-energy at constant flux(d) increase the co-energy at constant mmfI have been asked this question at a job interview.This key question is from Singly Excited Magnetic Systems in portion Magnetic Circuits of Electrical Machines
Answer» The correct choice is (d) INCREASE the co-energy at constant MMF The BEST explanation: FE = (∂Wfld^1 (i,x))/∂x = (∂Wfld^1 (F,x))/∂x, the positive sign before ∂Wfld^1 indicates that force fe acts in a direction as to tend to increase the co-energy at constant mmf.

5.	The electromagnetic force and/or torque, developed in any physical system, acts in such a direction as to tend to ____________(a) decrease the magnetic stored energy at constant mmf(b) decrease the magnetic stored energy at constant flux(c) increase the magnetic stored energy at constant flux(d) increase the magnetic stored energy at constant currentThis question was posed to me in unit test.This intriguing question originated from Singly Excited Magnetic Systems topic in section Magnetic Circuits of Electrical Machines
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6.	For a linear electromagnetic circuit, which of the following statement is true?(a) Field energy is less than the Co-energy(b) Field energy is equal to the Co-energy(c) Field energy is greater than the Co-energy(d) Co-energy is zeroThis question was addressed to me by my college professor while I was bunking the class.Question is taken from Singly Excited Magnetic Systems topic in chapter Magnetic Circuits of Electrical Machines
Answer» CORRECT OPTION is (B) Field energy is EQUAL to the Co-energy Easy EXPLANATION: Wfld=Wfld^1=1/2 φi=1/2 F∅.

7.	When a current of 5A flows through a coil of linear magnetic circuit, it has flux linkages of 2.4 wb-turns. What is the energy stored in the magnetic field of this coil in Joules?(a) 6(b) 12(c) 1.2(d) 2.4The question was asked in an internship interview.Question is from Singly Excited Magnetic Systems topic in section Magnetic Circuits of Electrical Machines
Answer» CORRECT option is (a) 6 The EXPLANATION: Wfld = 1/2 φi =1/22.4*5 = 6 JOULES.

8.	Magnetic stored energy density for iron is given by ______(a) 1/2 B/μ(b) 1/2 B^2 μ(c) 1/2 ∅^2 Rl(d) 1/2 B^2/μI have been asked this question in homework.This intriguing question comes from Singly Excited Magnetic Systems in portion Magnetic Circuits of Electrical Machines
Answer» Right OPTION is (d) 1/2 B^2/μ The explanation: Magnetic stored ENERGY DENSITY for iron is GIVEN as wfld=Wfld/((Length of the magnetic path through Iron)(Iron area normal to the magnetic FLUX))=1/2(F∅)/(lengthArea)=1/2F/length∅/area=1/2H*B Also, H = B/μ,thus wfld=1/2B^2/μ.

9.	The energy stored in a magnetic field is given by ____________ where L=self-inductance and Rl=reluctance.(a) 1/2 Li^2(b) 1/2 (mmf*Rl)^2(c) 1/2∅Rl(d) 1/2 φ^2iThis question was addressed to me at a job interview.Asked question is from Singly Excited Magnetic Systems in portion Magnetic Circuits of Electrical Machines
Answer» RIGHT OPTION is (a) 1/2 Li^2 The EXPLANATION is: We KNOW that Wfld=1/2 φi and L=φ/i, THUS Wfld=1/2 Li^2.

10.	For a toroid to extract the energy from the supply system, the flux linkages of the magnetic field must be ________(a) zero(b) changing or varying(c) constant(d) any of the mentionedI had been asked this question at a job interview.My question comes from Singly Excited Magnetic Systems topic in portion Magnetic Circuits of Electrical Machines
Answer» The correct CHOICE is (B) changing or varying Easiest explanation: dWelec=idφ=eidt, where dWelec = differential electrical energy to coupling FIELD, and if the flux LINKAGES are EITHER constant or zero, i.e, dφ=0, then dWelec=0.

11.	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 magnetic field(b) stored in the electric field(c) divided equally between the magnetic and electric fields(d) zeroThe question was posed to me by my school principal while I was bunking the class.My query is from Principle of Energy Conversion topic in section Magnetic Circuits of Electrical Machines
Answer» CORRECT ANSWER is (a) STORED in the magnetic field To ELABORATE: As the movable part is FIXED, Wmech = 0, we know, Welec = Wmech + Wfld, therefore, Welec = Wfld.

12.	The developed electromagnetic force and/or torque in electromechanical energy conversion system, acts in such a direction that tends to ___________(a) increase the stored energy at constant mmf(b) decrease the stored energy at constant mmf(c) decrease the co-energy at constant mmf(d) increase the stored energy at constant fluxI have been asked this question in quiz.I need to ask this question from Principle of Energy Conversion in portion Magnetic Circuits of Electrical Machines
Answer» Right answer is (B) decrease the stored energy at constant mmf Easiest explanation: FE = -(∂Wfld (φ,X))/∂x = -(∂Wfld (∅,x))/∂xand Te = -(∂Wfld (φ,θ))/∂θ = -(∂Wfld(∅,θ))/∂θ.

13.	The formula for energy stored in the mechanical system of linear motion type is ______(a) 1/2 Jwr^2(b) 1/2 mv^2(c) 1/2 mv(d) Jwr^2The question was posed to me in an online interview.My question is from Principle of Energy Conversion in portion Magnetic Circuits of Electrical Machines
Answer» Correct answer is (b) 1/2 mv^2 For EXPLANATION: ENERGY STORED is kinetic energy, since the system is of LINEAR MOTION.

14.	The energy storing capacity of magnetic field is about ________ times greater than that of electric field.(a) 50,000(b) 25,000(c) 10,000(d) 40,000This question was addressed to me in examination.This intriguing question comes from Principle of Energy Conversion topic in division Magnetic Circuits of Electrical Machines
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15.	What is the coupling field used between the electrical and mechanical systems in energy conversion devices?(a) Magnetic field(b) Electric field(c) Magnetic field or Electric field(d) None of the mentionedI got this question by my college director while I was bunking the class.This interesting question is from Principle of Energy Conversion in portion Magnetic Circuits of Electrical Machines
Answer» The correct option is (C) Magnetic field or Electric field For explanation I WOULD say: EITHER electric field or magnetic field can be used, however most commonly we USE magnetic field because of its greater energy storage CAPACITY.

16.	An electro-mechanical energy conversion device is one which converts _______(a) Electrical energy to mechanical energy only(b) Mechanical energy to electrical energy only(c) Electrical to mechanical and mechanical to electrical(d) None of the mentionedThe question was asked at a job interview.This question is from Principle of Energy Conversion in chapter Magnetic Circuits of Electrical Machines
Answer» CORRECT choice is (c) Electrical to mechanical and mechanical to electrical The best explanation: The operating principles of electrical to mechanical and mechanical to electrical conversion devices are SIMILAR, hence, the common name electro-mechanical device. However, their structural DETAILS DIFFER depending on their function.