How to find the magnetic flux of this magnet?

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Discussion Overview

The discussion centers on finding the magnetic flux of a cylindrical magnet as it passes through a coil. Participants explore the complexities of magnetism, particularly in relation to the calculation of magnetic flux and the behavior of the magnetic field in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks a conservative approximation of magnetic flux using the formula ΦB = B · A, questioning how to account for the non-constant magnetic field over the loop.
  • Another participant notes that if the coil is not loaded, the flux in the magnet will not change as it passes through the coil, resulting in no current flow.
  • There is a discussion about the magnetic flux density (B) changing over the loop while the flux (Φ) remains constant, with a focus on the cross-sectional area of the B-field.
  • A participant expresses confusion about the concept of the "cross section area" of the B-field and requests clarification on how it changes over the loop.
  • One participant argues against the notion of a "cross section area" for the B-field, stating that it is infinite and illustrates their point with a diagram showing the spread of the magnetic field outside a solenoid.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of the magnetic field and the implications for calculating magnetic flux. There is no consensus on the interpretation of the cross-sectional area in relation to the magnetic field.

Contextual Notes

Participants highlight the complexity of the magnetic field's behavior and the assumptions involved in calculating magnetic flux, particularly regarding the loading of the coil and the nature of the magnetic field outside the magnet.

radaballer
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I am looking to find the magnetic flux of a cylindrical magnet as it passes through a coil. I am aware of the complexity of magnetism, however, i am only looking for a conservative approximation of the magnetic flux. I found the formula ΦB = B · A, but is my understanding that the magnetic field will not be constant over the loop. How do I account for this in the calculation? Also, is the equation asking for the cross-sectional area of the solenoid, or the area of the actual piece of wire used to make the coil?
 
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More information is needed: Is the coil loaded somehow? If not, the flux in the magnet will not change when it passes through the coil, no current will flow in the coil.
radaballer said:
I found the formula ΦB = B · A, but is my understanding that the magnetic field will not be constant over the loop.
The magnetic flux density (B) will change over the loop, but the flux (Φ) will not. The "cross section area" of the B-field will change over the loop, being expanded outside the magnet.
radaballer said:
is the equation asking for the cross-sectional area of the solenoid
Yes, presumably.
 
Hesch said:
More information is needed: Is the coil loaded somehow? If not, the flux in the magnet will not change when it passes through the coil, no current will flow in the coil.

The magnetic flux density (B) will change over the loop, but the flux (Φ) will not. The "cross section area" of the B-field will change over the loop, being expanded outside the magnet.

Yes, presumably.
Ok, I am having a hard time understanding what you mean by "the "cross section area" of the B-field will change over the loop, being expanded outside the magnet." Can you explain how this happens?
 
radaballer said:
I am having a hard time understanding what you mean by "the "cross section area" of the B-field will change over the loop, being expanded outside the magnet
Actually I cannot speak of a "cross section area" as for the B-field because it is infinite. Some extremely sensitive instrument could sense your magnet field on the moon.

But this illustrates what I mean:

ad47be8696067dd04e99f783722ecfe7.png


It is a solenoid, but it could be your magnet as well. You can see that the field-curves spread out outside the solenoid, indicating that the B-field is weaker here. Contrary the are close to each other inside the solenoid/magnet.
 

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