Magnetic strength cannot be measured

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    Magnetic Strength
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Discussion Overview

The discussion centers around the concept of measuring magnetic strength, particularly in relation to the absence of magnetic monopoles and the implications for defining a unit of measurement for magnetic force. Participants explore theoretical aspects and definitions related to magnetic poles and forces.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why magnetic force cannot be measured and notes the lack of a unit for magnetic strength (p).
  • Another participant suggests that the absence of magnetic monopoles prevents the definition of a unit for magnetic strength, comparing it to electric charges which can be defined as positive or negative.
  • A third participant agrees with the previous point, emphasizing that while electric and gravitational forces have defined unit charges and masses, a unit magnetic pole has not been established.
  • One participant introduces the concept that magnetic pole strength can be expressed in terms of magnetization and area, providing a specific unit (gauss-cm²) and suggesting that the end of a bar magnet behaves like a point monopole under certain conditions.

Areas of Agreement / Disagreement

Participants express a general agreement on the difficulty of defining a unit for magnetic strength due to the lack of magnetic monopoles. However, there are differing views on how to approach the measurement of magnetic pole strength, indicating that the discussion remains unresolved.

Contextual Notes

Limitations include the dependence on definitions of magnetic strength and the implications of using different units in various contexts. The discussion does not resolve the question of how to measure magnetic force definitively.

bobsmith76
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I don't get the following passage from my textbook. Why can't the magnetic force be measured? I don't see why there is no unit for p.

If one pole of a long, thin bar magnet is placed in the vicinity of one pole of another long, thin bar magnet, Coulomb’s magnetic force law states: The magnetic force F between one pole of magnetic strength p1 and another pole of magnetic strength p2 is inversely proportional to the square of the distance r between
them, or F ∝ p1p2/2 . It is not possible, however, to find a proportionality constant, because it is not possible to define a unit for p, a magnetic monopole
 
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I *think* it's just saying that because there are no magnetic monopoles, which would be an object that is only 1 pole of a magnet, aka a "magnetic charge", we cannot define a constant to it's strength like we can with the electric force, which does have single charges of both positive and negative. Not sure though.
 
I would agree with Drakkith. In electricity and gravitation it is possible to define a unit charge and a unit mass but I have never met a definition of a unit magnetic pole.
 
The magnetic pole strength at the end of a bar magnet equals MA, where M is the magnetization and A the area lof the end in Gaussian units. The unit of pole strength is
gauss-cm^2. The end acts like a point monopole when its area is small compare to r^2.
 

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