Cross product evaluation (for the Lorentz Force).

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Discussion Overview

The discussion revolves around the evaluation of the cross product in the context of the Lorentz Force, specifically focusing on the expression for the vector \(\vec{C} = \vec{E} \times \vec{B}\). Participants explore the mathematical formulation of the cross product and its implications in physics, particularly in relation to charged particle dynamics in electric and magnetic fields.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents the Lorentz Force equation and expresses a desire to calculate \(\vec{C} = \vec{E} \times \vec{B}\) using their definitions of \(\vec{E}\) and \(\vec{B}\).
  • Another participant questions the origin of a specific equation related to the cross product and suggests using standard methods to express the cross product via components.
  • A later reply asserts that the equation in question derives from the property \(\vec{E} \times \vec{B} = -\vec{B} \times \vec{E}\), but this is met with resistance from the original poster.
  • There is a clear expression of frustration from one participant towards another, indicating a breakdown in communication and a desire to cease further interaction.

Areas of Agreement / Disagreement

Participants do not reach consensus on the derivation of the equation in question, and there is evident disagreement regarding the appropriateness of responses and the nature of the discussion.

Contextual Notes

There are unresolved questions regarding the derivation of the cross product equation and the assumptions underlying the participants' statements. The discussion reflects a mix of technical inquiry and interpersonal conflict.

rogerk8
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Let's say we have:

\vec{E}=E_x\vec{i}_x+E_y\vec{i}_y+E_z\vec{i}_z

and

\vec{B}=B_x\vec{i}_x+B_y\vec{i}_y+B_z\vec{i}_z

and the Lorentz Force

0=q(\vec{E}+\vec{v}X\vec{B})

which due to

\vec{E}X\vec{B}=\vec{B}X(\vec{v}X\vec{B})=vB^2-B(\vec{v}\cdot \vec{B})

and transverse components only, gives

v_{gc}=\frac{\vec{E}X\vec{B}}{B^2}

where Vgc is the guiding center drift of the charged particles in a magnetic field with an electric field.

My question now is how to calculate

\vec{C}=\vec{E}X\vec{B}

I could have chosen pure math for this but I'm tired of theory that is hard to see the practical use of.

So what is C, with my definitions of E & B?

And how do I calculate it (the manitude and resulting direction is easy but I whish to see it in math)?

Does anyone want to help me refresh this knowledge?

Roger
 
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rogerk8 said:
which due to

\vec{E}X\vec{B}=\vec{B}X(\vec{v}X\vec{B})=vB^2-B(\vec{v}\cdot \vec{B})
I don't understand where that equation comes from.
My question now is how to calculate

\vec{C}=\vec{E}X\vec{B}
With the standard way to express the cross-product via components. You can find the formula in literally every textbook, in all the wikipedia articles and in thousands of other websites related to the cross-product..
 
mfb said:
I don't understand where that equation comes from.
With the standard way to express the cross-product via components. You can find the formula in literally every textbook, in all the wikipedia articles and in thousands of other websites related to the cross-product..

Simple, the equation comes from

\vec{E}X\vec{B}=-\vec{B}X\vec{E}

Please don't answer (or whatever you think you are trying to do) any more of my posts.

I don't like you.

/Roger
 
rogerk8 said:
Please don't answer (or whatever you think you are trying to do) any more of my posts.

I don't like you.

You don't like being reminded of reality by a professional working physicist? Hmm
 
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Roger has left the building, so this thread is now closed.
 

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