14/03/2020

Electromagnetic Induction Interview Question Answer


1
Explain the term : Electromagnetic induction


Electro – magnetic induction
  • When the magnetic flux linking with a conductor changes, an emf is induced in the conductor. 
  • This phenomenon is called as electromagnetic induction.


2
State the first and second laws of electromagnetic induction.


Faraday’s first law
  • Whenever the conductor cuts the flux, an emf is induced in it.

Faraday’s second law
  • The magnitude of the induced emf is directly proportional to rate of change of flux linkages.

 e = – N ( dФ / dt )
  • The minus sign is due to the Lenz’s law


3
State the Fleming’s left hand rule.


Fleming’s left hand rule
  • Keep the left hand such that first finger, middle finger and thumb are mutually perpendicular.
  • If the first finger shows the direction of the magnetic field, middle finger shows direction of the current then thumb indicated direction of the force.


5
Explain the term : Dynamically Induced emf


Dynamically induced emf
  • When the induced emf in the coil or conductor by movement of either magnetic field or conductor, it is called as dynamically induced emf.


6
State the value of induced emf if the conductor is move parallel to the direction of flux.


  • If the conductor is move parallel to the direction of the flux then no flux is cut by the conductor therefore induced emf is zero.


7
Explain : Statically induced emf , Self induced emf and Mutual induced emf


Statically induced emf
  • The induced emf by variation in the flux when conductor is held stationary is called as statically induced emf.

Self induced emf
  • The induced emf in the coil due to change of flux linking with own turns in the coil are called as self induced emf.

Mutual induced emf
  • The induced emf in the coil due to flux linking in the coil by other nearby coil is called as mutual induced emf.


8
Describe the property of inductor.


Property of inductor
  • The property of the inductor is to oppose the change of current through it. The inductor does not affect the value of direct current.


9
What is value of self inductance when direct current is passing through coil? Comment on it


Self inductance on DC
  • When direct current passing through inductor, the self inductance of the coil becomes zero.

            VL  =  L di/dt
            VL  = Induced emf
               L = Inductance
            di / dt = Rate of change of current i.e. alternating current

10
Why chock coil is wound with small air gap?


Choke coil
  • The choke coil is wound with small air – gap because the air gap reduces the value of inductance slightly.
  • The B – H curve of the choke coil becomes linear over a wide range of current due to presence of air gap.


11
Which coil has high value of inductance for same number of turns?
Air core coil or magnetic core coil


Magnetic core coil

12
Explain the term : Mutual inductance


Mutual inductance
  • When two circuits are connected to common magnetic circuit, it is said to be two circuits are coupled to each other.
  • The circuit element used to represent magnetic coupling between two circuits is called as mutual inductance.


13
Explain the term : Co – efficient of coupling


Coefficient of coupling
  • The small flux which is produced by one coil links with other coil is known as coefficient of coupling between two coils. 
  • It is always less than unity.


14
What do you understand if the coefficient of coupling is zero?


Co – efficient of coupling
  • When the flux in one coil does not link with the other coil, two coils are separate and therefore the coefficient of coupling is zero.
  • The coefficient between two coils are related to

             K = M / √ L1 L2

15
What do you mean by following terms : Two coils are ( a ) Tightly coupled ( b ) Loosely coupled and ( c ) Isolated


( a ) Tightly coupled
  • If the flux produces by one coil completely links with other coil then two coils are said to be tightly coupled.

( b ) Loosely coupled
  • The small values of flux of one coil links with other coil then two coils are called as loosely coupled.

( c ) Isolated
  • If the flux produces by one coil does not link with other coil then two coils are called as isolated.


16
Which phenomenon is responsible for energy stored in the current carrying coil ( Electro – magnet ) ?


Energy stored in the coil
  • When current is passing through the coil from minimum to maximum value, this current is opposed by self induced emf due to change of current. 
  • Some energy is needed to overcome this opposition actually. 
  •  This energy is stored in the magnetic field of the current carrying coil.


17
Give reason : The current does not rise immediately in the inductor circuit.


The current in the inductor coil does not rise immediately due to self inductance of the coil.

18
Explain the term : Time – constant of R – L circuit


Time constant of R – L circuit
  • The time required for the current to attain 63.2% of the final value is known as time – constant of the R – L circuit.
  • The time required for the current to attain 36.8% of the initial value during decaying period is known as time – constant of the R – L circuit.

       Time – constant = L / R

19
Describe the effect on time constant of R – L circuit when the value of resistance changes.


Greater the value of resistance, lesser is the time taken by the R – L circuit to reach its final value and vice – versa.

20
State the law of conservation of energy.


Law of conservation of energy
  • Energy is neither created nor destroyed, some of the all energy in the system is constant.


21
State the Lenz’s law.


Lenz’s law
  • The induced current due to electromagnetic induction always flow in the such direction that it produces a current in such direction that magnetic field opposes the change which produce it.


22
State the Flat left hand rule.


Flat left hand rule
  • It states that the left hand palm is kept flat on horizontal axis. 
  • If the flux direction enters the palm from North pole, four finger shows direction of current then the thumb indicates the direction of force acts on the conductor.


23
How to know direction of magnetic field?


Magnetic field
  • The direction of magnetic field can be determined by right hand rule.
  • It states that current carrying conductor is held in right hand such that the thumb indicates the direction of current.
  • If the direction of current upward, the four finger shows direction of magnetic field which is anticlockwise.
  • If the direction of current downward, the four finger shows direction of magnetic field which is clockwise.


24
What do you mean by solenoid?


Solenoid
  • The current carrying coil wound in the form of spiral about on axis is called as solenoid.


25
State the helix rule.


Helix rule
  • If the solenoid is held in the right hand in such manner that the four finger tips shows the direction of current flow, the outstretched thumb indicates North pole.




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