Why does the current have no ##\phi## component in a toroidal coil?

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Discussion Overview

The discussion revolves around the question of why the current in a toroidal coil has no ##\phi## component. Participants explore the implications of cylindrical coordinates and the behavior of current in a toroidal geometry, addressing theoretical models, approximations, and the physical representation of the coil.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that the current has no ##\phi## component based on the geometry of the toroidal coil, where the wires do not extend in the ##\phi## direction.
  • Others argue that while the ##\phi## component can be minimized by increasing the number of turns per unit length, it is not entirely zero unless certain conditions are met.
  • Several participants mention that the situation can be treated as an approximation, suggesting that the model simplifies the physical reality of the toroid.
  • A participant questions how the limit of turns per unit length approaching infinity relates to the current approaching zero.
  • There are calls for visual aids to better understand the implications of increasing the number of turns and the resulting current distribution.
  • Some participants express confusion regarding the relationship between the geometry of the toroid and the current's behavior, indicating a need for clarification on the modeling approach.
  • One participant suggests that the discussion is becoming convoluted and that the original question may have been misinterpreted.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of the ##\phi## component of the current. While some agree on the approximation of zero current in the ##\phi## direction, others maintain that this is contingent on specific conditions and modeling choices, leading to ongoing debate.

Contextual Notes

Limitations in the discussion include varying interpretations of the toroidal model, assumptions about the wire's geometry, and the implications of mathematical limits on current behavior. The discussion also reflects differing levels of comfort with calculus and mathematical modeling among participants.

  • #31
Adesh said:
But in spite of all these I can't seem to understand how the current have no ##\phi## component. Well, in that toroid we have current going on in circles and really I don't anything more than this.

Please help me!
You can make the ##\phi## component of current = 0 by the way you wind the wire.

If you use just one winding then obviously there must be a ##\phi## component of current since each turn of wire is connected to the next by a short run of ##\phi## section to get around the toroid's periphery.

But if you do 2 windings (layers) the second winding's sections' current can cancel out the first if properly wound.
 
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  • #32
rude man said:
You can make the ##\phi## component of current = 0 by the way you wind the wire.

If you use just one winding then obviously there must be a ##\phi## component of current since each turn of wire is connected to the next by a short run of ##\phi## section to get around the toroid's periphery.

But if you do 2 windings (layers) the second winding's sections' current can cancel out the first if properly wound.
Yes, I got it thanks. You know my main problem was that I was unable to decompose a circle (that is the loop of a wire wound around the toroid) into just ##\hat{r}## and ##\hat{z}## components, because you know when we draw a circle in ##xy## plane we decompose it’s line elements into ##\hat{r}## and ##\hat{\phi}## directions (if we use polar coordinates) . So, it was hard for me to imagine such a situation where we had no ##\phi## component.
 
  • #33
Adesh said:
Yes, I got it thanks. You know my main problem was that I was unable to decompose a circle (that is the loop of a wire wound around the toroid) into just ##\hat{r}## and ##\hat{z}## components, because you know when we draw a circle in ##xy## plane we decompose it’s line elements into ##\hat{r}## and ##\hat{\phi}## directions (if we use polar coordinates) . So, it was hard for me to imagine such a situation where we had no ##\phi## component.
Right. The trick is two windings with the second nulling the ##\phi ## component from the first.
 
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