Calculating Magnet Deceleration in a Moving Coil

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Discussion Overview

The discussion revolves around calculating the deceleration of a magnet as it moves through a coil, particularly in the context of induced current and electromagnetic principles. Participants explore the relationship between the magnet's motion, the induced electric field, and the resulting forces acting on the magnet.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant inquires about the deceleration of a magnet moving through a coil and questions whether it will decelerate at all, citing a personal experience with a mechanically-powered flashlight.
  • Another participant asserts that the magnet will decelerate and suggests calculating the energy produced to determine the kinetic energy lost by the magnet.
  • A third participant references Lenz's Law, relating it to conservation of energy and momentum, indicating a theoretical framework for understanding the deceleration.
  • Further contributions explain that the induced electric field causes a current in the coil, which generates an opposing magnetic field that decelerates the magnet, though the exact equation for deceleration is noted as not immediately obvious.
  • One participant mentions the creation of positive and negative voltage due to the EMF generated as the coil interacts with the magnetic field.
  • Another participant suggests a simplified model treating the magnet or coil as a harmonic oscillator, while also questioning the terminology used for EMF.
  • A later reply reiterates the initial question, clarifying assumptions about the type of magnet and its motion through the coil.

Areas of Agreement / Disagreement

Participants express differing views on the specifics of calculating deceleration and the underlying principles, indicating that multiple competing perspectives remain without a consensus on the exact approach or equations to use.

Contextual Notes

Some participants note that the actual equation for deceleration may depend on the specific form of the magnetic field created by the magnet, suggesting that assumptions about the magnetic field strength and configuration could influence the discussion.

Ponkeli
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Hi!

I'm a new face here and have an easy question.

I know how to calculate induced current when magnet moves through coil (it's E=BLv) but how do you calculate how much a magnet will decelerate when it goes through the coil? Will it decelarate at all?

I have one of those mechanically-powered flashlights and the magnet won't slow a bit probably because the strength of magnetic field isn't so great.

Thanks.
 
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Yes it will decelerate. The easiest way to calculate is the Energy produced. If you know the power consumed by the light, you know how much kinetic energy the magnet had to lose.
 
This is Lenz's Law and it is the electromagnetic formulation of Newton's Third Law, in other words conservation of energy and momentum.
 
Once you've calculated the electric field through the coil, that electric field will make charges go round the coil, creating a current.
The current going round the coil creates its own magnetic field (just like in a solenoid) that opposes the magnetic field of the magnet.
This opposing magnetic field causes a force on the magnet, decelerating it.
The actual equation for this deceleration is not immediately obvious from the laws of electromagnetism... I guess it depends on the form of the magnetic field created by the magnet...
 
Correct OP, his is the reason why positive and negative voltage gets created from the EMF of the coil passing in and out through the magnetic field.
 
If you were really anal you could treat the magnet (or the coil, that relative stuff) like a simple harmonic oscillator. It would be a perversion of what's really going on with the muscles in your hand but it would be easier. The last statement really sounds a bit strange, sorry.

Anyways, length of the path of the magnet, get a good rhythm going, time it... weird stuff.

And that E is EMf?
 
Ponkeli said:
Hi!

I'm a new face here and have an easy question.

I know how to calculate induced current when magnet moves through coil (it's E=BLv) but how do you calculate how much a magnet will decelerate when it goes through the coil? Will it decelarate at all?

I have one of those mechanically-powered flashlights and the magnet won't slow a bit probably because the strength of magnetic field isn't so great.

Thanks.

Oh.
I was also assuming you had the commercial model with the cylindrical magnet that moves back and forth. It bumps a spring on each side to change direction and go back through the coil... I did not realize what you were looking for, WHEN IT GOES THROUGH THE COIL. My bad, as we say.
 

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