Why the induced emf is always negative?

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Discussion Overview

The discussion revolves around the nature of induced electromotive force (emf) as described by Faraday's law and Lenz's law. Participants explore the implications of these laws, particularly focusing on the assertion that induced emf is always negative and the conditions under which this occurs. The conversation includes theoretical interpretations and references to external resources.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants reference Faraday's law and assert that the induced emf is always negative, citing a specific article for support.
  • Others explain Lenz's law, suggesting that the induced emf creates an opposing magnetic field to the one inducing it, linking this to the conservation of energy.
  • A participant questions the conservation of energy aspect, asking for clarification on what is being conserved.
  • One participant argues that if the induced emf were in the same direction as the circuit's emf, it would lead to an exponential increase in voltage and current, which is not feasible, thus supporting the idea that the induced emf must oppose the change.
  • Another participant challenges the interpretation of the negative sign in Faraday's law, stating it does not imply that the emf or current always points in a negative direction, but rather that it opposes the change in magnetic flux.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the negative sign in induced emf and the implications of Lenz's law. There is no consensus on the explanations provided, and multiple competing interpretations remain present in the discussion.

Contextual Notes

Some claims rely on specific interpretations of conservation of energy and the definitions of emf and magnetic flux, which may not be universally agreed upon. The discussion includes references to external resources that may influence participants' understanding.

Physicsissuef
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Hi! I read this article about Faraday's law, which states, that the emf will be always negative, by the formula, is this http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html"
 
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Lenz law supplies that answer. It basically states that the EMF that is induced will be in such a way to create an opposing magnetic field to the one inducing the EMF. This law stems from the conservation of energy.
 
Ronnin said:
Lenz law supplies that answer. It basically states that the EMF that is induced will be in such a way to create an opposing magnetic field to the one inducing the EMF. This law stems from the conservation of energy.
Conservation of energy of what?
Btw- Look at this http://www.youtube.com/watch?v=stUDqGzpev8". The voltage is not negative, always.
 
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Physicsissuef said:
Conservation of energy of what?

Simply put, if the induced emf was in the direction of the emf of the circuit, then the inductor would increase the voltage in the circuit. Which would increase the current flowing across the inductor. As such, it would further increase the induced emf [they are proportional] as B = \mu_o NI. This increase would further increase the the emf and as such, the voltage should rise exponentially. Which would mean, we could derive infinite energy from the system.

as we know that this is not possible, the induced emf cannot be in the same direction. Although, this cannot be used to prove Lentz law, but is helpful for understanding the situation.
 
Physicsissuef said:
Btw- Look at this http://www.youtube.com/watch?v=stUDqGzpev8". The voltage is not negative, always.

The negative sign in Faraday's law (Lenz's law) does not mean that the EMF (or current) always points in some "negative" direction. It means that the current always flows in a way to oppose the change in flux, which is nicely illustrated in that video clip.
 
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