Why Does Induced EMF Change in Generators but Not Moving Conductors?

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Discussion Overview

The discussion revolves around the differences in induced electromotive force (emf) in generators compared to moving conductors. It explores the theoretical underpinnings of induced emf, particularly in relation to magnetic flux changes and the conditions under which emf is generated.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that constant change in magnetic flux in a moving conductor leads to constant induced emf, while sinusoidal change in magnetic flux in a rotating generator results in sinusoidal induced emf.
  • Another participant clarifies that a conductor moving at constant speed through a constant magnetic field does not generate constant emf, emphasizing the need for a time rate of change of flux enclosed by the conductor.
  • It is noted that induced voltage is governed by Faraday's law, which involves the integration of magnetic field over the area enclosed by a conducting loop.
  • One participant states that if a conducting loop moves through a constant magnetic field, there is no induced emf due to the lack of change in the flux enclosed by the loop.
  • There is a discussion about the nature of the "moving conductor," with some participants indicating that it refers to a movable piece of metal rather than the entire loop.
  • A participant introduces the concept of an expanding loop, suggesting that the induced emf can be expressed in terms of the velocity and length of the conductor, leading to a constant emf if velocity is constant.

Areas of Agreement / Disagreement

Participants express differing views on the conditions under which induced emf occurs, particularly regarding the movement of conductors and the nature of magnetic flux changes. The discussion remains unresolved with multiple competing views present.

Contextual Notes

There are limitations related to the assumptions about the nature of the magnetic fields and the configurations of the conductors involved in the discussion. The dependency on specific definitions and conditions for induced emf is also noted.

leojun
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why does induced emf change in case of generators but remains constant in case of moving conductor?
 
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after thinking for a while,i myself came to the conclusion that constant change in magnetic flux(in moving conductor with constant vel) causes constant induced emf and sinusoidal change in magnetic flux(in rotating generator) causes sinusoidal induced emf...:);)
 
The second part of your question is a bit confusing. A conductor does not generate constant emf if it moves at constant speed through a constant magnetic field. There has to be a time rate of change of flux enclosed by the conductor.

Induced voltage is governed by Faraday's law: [itex]\oint \vec{E}\cdot d\vec{s} = -\frac{d}{dt}\int \vec{B}\cdot d\vec{A}[/itex]

Since in a rotating generator, [itex]\vec{B}\cdot d\vec{A}[/itex] is integrated over the area enclosed by a conducting loop in the armature, the right side keeps changing if the loop rotates in a fixed magnetic field. So the induced voltage (the left side: the line integral of the electric field over the path around the loop) keeps changing.

If a conducting loop moves through a constant magnetic field there is no induced emf. This is because there is no change in the flux enclosed by the loop.

AM
 
Andrew Mason said:
If a conducting loop moves through a constant magnetic field there is no induced emf. This is because there is no change in the flux enclosed by the loop.

AM

Not the whole loop moves, but one side only in the experiments showing induced voltage in a moving straight piece of metal.

ehild
 
yup,the conductor here means the movable piece of metal...not the whole circuit.
 
ehild said:
Not the whole loop moves, but one side only in the experiments showing induced voltage in a moving straight piece of metal.

ehild
Ok. So the "moving conductor" is really an expanding loop in which dA/dt = velocity x length of the conductor. In that case [itex]\xi = -\frac{d}{dt}\int\vec{B}\cdot d\vec{A}[/itex] = -Bvl which is constant if v is constant.

AM
 
Andrew Mason said:
Ok. So the "moving conductor" is really an expanding loop in which dA/dt = velocity x length of the conductor. In that case [itex]\xi = -\frac{d}{dt}\int\vec{B}\cdot d\vec{A}[/itex] = -Bvl which is constant if v is constant.

AM
Yes.

ehild
 

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