logo
  • Home
  • About
  • Training
  • Programming
  • CS
  • IT
  • IS
  • ECE
  • EEE
  • EE
  • Civil
  • Mechanical
  • Chemical
  • Metallurgy
  • Instrumentation
  • Aeronautical
  • Aerospace
  • Biotechnology
  • Agriculture
  • MCA
  • BCA
  • Internship
  • Contact

Electrical Machines Multiple Choice Questions | MCQs | Quiz

Electrical Machines Interview Questions and Answers
Pratice Electrical Machines questions and answers for interviews, campus placements, online tests, aptitude tests, quizzes and competitive exams.

Get Started

•   Energy Principles
•   Singly Magnetic System
•   Reluctance Motor
•   Doubly Magnetic System
•   Synchronous Machines
•   Singly Electric Systems
•   Torque Equations
•   Rotating Machines Terms
•   Rotating Magnetic Field-1
•   Rotating Magnetic Field-2
•   Rotating EM - 1
•   Rotating EM - 2
•   Rotating EM - 3
•   Generated Emfs
•   Losses and Efficiency-1
•   Losses and Efficiency-2
•   Machine Ratings
•   Cooling(Loss Dissipation)
•   Machine Applications
•   Commutator Action
•   Armature Generation
•   DC Machines Torque
•   DC Machines Circuits
•   Excitation Methods
•   MMF & Flux Waveforms
•   Compensation Winding
•   DC Machines Testing
•   DC Machine Applications
•   Generator Characteristics
•   Rotating Amplifiers
•   Motors Characteristics
•   DC Motors Basics
•   DC Motors Speed Control
•   DC Motors Magnet
•   EMF Polygon - 1
•   EMF Polygon - 2
•   Non-Salient Machines
•   Distributed Windings
•   Synchronous Machines
•   Flux & MMF Phasors
•   Synchronous Operation
•   Synchronous Controls
•   Salient Pole Machines
•   Characteristics
•   Xd & Xq Measurement
•   Applications
•   Cylindrical Rotor
•   Voltage Regulation
•   Alternator Characteristics
•   Motors Phasor Diagram
•   Motor Power Factor
•   Motors Basics
•   Inductive Impedance - 1
•   Inductive Impedance - 2
•   Efficiency
•   Losses & Efficiency
•   Power & Torque
•   Synchronous Stability
•   Damper Winding
•   Induction Motor
•   Operation Principles
•   MMF Phasors & Waves
•   Rotor Frequency
•   EMF, Current & Power
•   Induction Motor Phasor
•   Equivalent Circuit
•   Circuit Analysis
•   Motor Characteristics
•   Circuit Parameters
•   Three Phase Motor
•   Induction Generator
•   Polyphase Induction
•   Induction Diagrams
•   Polyphase Motors - 1
•   Polyphase Motors - 2
•   Armature Windings
•   Transformer Construction
•   Ideal Two Winding
•   Phasor Diagrams
•   Transformer Circuit
•   Open & Short Circuit Test
•   Voltage Regulation
•   Transformer Efficiency
•   Single Phase
•   Magnetically Coupled
•   Three Phase Transformer
•   Autotransformers

« Prev Page
Next Page »

Electrical Machines Questions and Answers – Singly Excited Electric Field Systems

Posted on May 19, 2017 by Manish

This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Singly Excited Electric Field Systems”.

1. A parallel plate capacitor has a capacitance of 10μF. If the linear dimensions of the plates are doubled and distance between them is also doubled, the new value of capacitance would be __________
a) 10μF
b) 20μF
c) 5μF
d) 40μF
View Answer

Answer: b
Explanation: C1= 10μF = ε0A1/x1
C2= ε0A2/x2 , A2=4A1(as the linear dimensions are doubled, area increases by 4 times) and x2=2x1
⇒ C2= ε04A1/2x1 = 2∗10μF =20μF

2. A parallel plate capacitor is changed and then the DC supply is disconnected. Now plate separation is allowed to decrease due to force of attraction between the two plates. As a consequence __________
(i) charge on the plate increases
(ii) charge on the plates remain constant
(iii) capacitance C increases
(iv) capacitance C remains constant
(v) potential difference increases
(vi) potential difference decreases
(vii) energy stored decreases
(viii) energy stored increases

Which of the above statements are correct?
a) (i),(iii),(vi)
b) (ii),(iv),(viii)
c) (ii),(iii),(vi),(vii)
d) (ii),(iv),(v),(viii)
View Answer

Answer: c
Explanation: C= εA/x and as separation is decreased, capacitance increases. Also, C=q/v and as charge remains constant, voltage decreases. Similarly, energy stored, Wfld=1/2q2/c(x) and it decreases.

3. A parallel plate capacitor is charged and then the DC supply is disconnected. The plate separation is then increased. Between the plates,
(i) electric field intensity is unchanged
(ii) flux density decreases
(iii) potential difference decreases
(iv) energy stored increases

Which of the above statements are correct?
a) (i),(iv)
b) (ii),(iv)
c) (ii),(iii),(iv)
d) (i),(iii),(iv)
View Answer

Answer: a
Explanation: We know C=ε0A/x, as x increases, C decreases.
Charge(q) on plate remains constant and q=Cv implies v increases.
Energy stored, Wfld= 1/2q2/C(x), as C decreases, Wfld increases.
Similarly as q=DA and q,A remains constant, D doesn’t change and as electric field intensity is given by, E=D/ε0, E also doesn’t change.

4. The area of two parallel plates is doubled and the distance between these plates is also doubled. The capacitor voltage is kept constant. Under these conditions, force between the plates of this capacitor __________
a) decreases
b) increases
c) reduce to half
d) gets doubled
View Answer

Answer: c
Explanation: A2=2A1, x2=2x1, v2=v1, fe2=1/2v2dC(x)/dx2, C2=ε0A2/x2 ⇒ dC2/dx2= -ε0A2/x22
dC2/dx2= -2ε0A1/4x12 = -ε0A1/2x12 ⇒ f&e2= -1/2v12ε0A1/2x12= -1/2(fe1)
⇒ force reduces to half.

5. A parallel plate capacitor has an electrode area of 1000 mm2, with a spacing of 0.1 mm between the electrodes. The dielectric between the plates is air with a permittivity of 8.85∗10-12 F/m. The charge on the capacitor is 100 v. The stored energy in the capacitor is ____________
a) 44.3 J
b) 444.3 nJ
c) 88.6 nJ
d) 44.3 nJ
View Answer

Answer: d
Explanation: Wfld = 1/2 q2/C(x)
C(x) = ε0A/x = 8.85∗10-12∗100∗(10-3)2/0.1∗10-3 = 8.85∗10-12 F
Wfld = 1/2∗Cv = 1/2∗1002∗8.85∗10-12 = 44.3nJ

6. A parallel plate capacitor is connected to a DC source. Now the plates are allowed to move a small displacement under the influence of force of attraction between the two plates. As a result ____________
(i) charge on the plates increases
(ii) charge on plates remains constant
(iii) energy stored increases
(iv) energy stored remains constant
(v) electric field intensity is unchanged
(vi) flux density increases

Which of the above statements are correct?
a) (ii),(iv),(v)
b) (ii),(iii),(vi)
c) (i),(iii),(v)
d) (i),(iii),(vi)
View Answer

Answer: d
Explanation:C = ε0A/x ⇒ C ∝ 1/x ⇒ If the force if of attraction type, then x decreases and C increases.
q=Cv, v constant⇒ as C increases, q also increases. We also know that q=DA and if q increaes, D increases.
Finally, Wfld= 1/2 D2/ε0 and as D is increasing, Wfld increases.

7. The force produced by electric field in a singly excited energy conversion device, using electric field as coupling medium can be obtained by ___________
a) use of field energy function only
b) use of coenergy function only
c) any of the mentioned
d) none of the mentioned
View Answer

Answer: c
Explanation: fe = -∂Wfld(q,x)/∂x
fe = -∂Wfld1(q,x)/∂x

8. Charge and voltage associated with electric field are analogous, respectively to __________ and ___________ in magnetic field.
a) flux linkages and current
b) flux density and current
c) flux linkages and voltage
d) MMF and current
View Answer

Answer: a
Explanation: In magnetic field, the basic terms are flux linkages and current, which are responsible for energy conversion and in electric field, charge and voltage are basically responsible for energy conversion.
dWelec = ψi, for magnetic field
dWelec = vidt=vdq, for electric field.

9. Two parallel plates, each of area A = 1m2 are separated by a distance g. The electric field intensity between the plates is 3∗106 v/m. What is the force between the two plates?
a) 1/2π∗103 N
b) 1/8π∗103 N
c) 8π∗103 N
d) 0 N
View Answer

Answer: b
Explanation: When electric field is applied, the plates move towards each other because of force of attraction by a distance x ⇒ C= ε0A/(g-x)
Wfld(q,x) = 1/2 q2/C = 1/2 q2(g-x)/Aε0
fe= -∂Wfld(q,x)/∂x= 1/2q2x/Aε0
We know, q=DA=ε0EA and ε0 = 10-9/36Π
fe= 1/2 E2ε0A= 1/2∗(3∗106)2∗10-9/36Π∗1 = 1/8π∗103 N

Sanfoundry Global Education & Learning Series – Electrical Machines.
To practice all areas of Electrical Machines, here is complete set of 1000+ Multiple Choice Questions and Answers.

« Prev Page - Electrical Machines Questions and Answers – Elementary Synchronous Machines
» Next Page - Electrical Machines Questions and Answers – Torque Production and Dynamic Equations
« Electrical Machines Questions and Answers – Elementary Synchronous Machines
Electrical Machines Questions and Answers – Torque Production and Dynamic Equations »

Deep Dive @ Sanfoundry:

  1. Signals & Systems Questions and Answers
  2. Control Systems Questions and Answers
  3. Design of Steel Structures Questions and Answers
  4. Electronic Devices and Circuits Questions and Answers
  5. Electrical Engineering Questions and Answers
  6. Electrical Measurements Questions and Answers
  7. Fluid Mechanics Questions and Answers
  8. Electromagnetic Theory Questions and Answers
  9. Electric Circuits Questions and Answers
  10. Electrical Machines Questions and Answers
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer and SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage & Cluster Administration, Advanced C Programming, SAN Storage Technologies, SCSI Internals and Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him below:
LinkedIn | Facebook | Twitter | Google+

Best Careers

Developer Tracks
SAN Developer
Linux Kernel Developer
Linux Driver Developer
Linux Network Developer

Live Training Photos
Mentoring
Software Productivity
GDB Assignment
Sanfoundry is No. 1 choice for Deep Hands-ON Trainings in SAN, Linux & C, Kernel Programming. Our Founder has trained employees of almost all Top Companies in India such as VMware, Citrix, Oracle, Motorola, Ericsson, Aricent, HP, Intuit, Microsoft, Cisco, SAP Labs, Siemens, Symantec, Redhat, Chelsio, Cavium, ST-Micro, Samsung, LG-Soft, Wipro, TCS, HCL, IBM, Accenture, HSBC, Mphasis, Tata-Elxsi, Tata VSNL, Mindtree, Cognizant and Startups.

Best Trainings

SAN I - Technology
SAN II - Admin
Linux Fundamentals
Advanced C Training
Linux-C Debugging
System Programming
Network Programming
Linux Threads
Kernel Programming
Kernel Debugging
Linux Device Drivers

Best Reference Books

Computer Science Books
Algorithm & Programming Books
Electronics Engineering Books
Electrical Engineering Books
Chemical Engineering Books
Civil Engineering Books
Mechanical Engineering Books
Industrial Engineering Books
Instrumentation Engg Books
Metallurgical Engineering Books
All Stream Best Books

Questions and Answers

1000 C Questions & Answers
1000 C++ Questions & Answers
1000 C# Questions & Answers
1000 Java Questions & Answers
1000 Linux Questions & Answers
1000 Python Questions
1000 PHP Questions & Answers
1000 Hadoop Questions
Cloud Computing Questions
Computer Science Questions
All Stream Questions & Answers

India Internships

Computer Science Internships
Instrumentation Internships
Electronics Internships
Electrical Internships
Mechanical Internships
Industrial Internships
Systems Internships
Chemical Internships
Civil Internships
IT Internships
All Stream Internships

About Sanfoundry

About Us
Copyright
TOS & Privacy
Jobs
Bangalore Training
Online Training
SAN Training
Developers Track
Mentoring Sessions
Contact Us
Sitemap
© 2011 Sanfoundry