Help with unit vector for a magnetic field

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Homework Help Overview

The discussion revolves around the calculation of a magnetic field related to a charged particle, specifically a proton, and involves the evaluation of a cross product between the velocity vector and position vectors. Participants are examining the implications of the charge's position and velocity in relation to the magnetic field's direction.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants are attempting to evaluate the cross product of vectors and are questioning the signs and results of their calculations. There are inquiries about the necessity of a magnetic field and the completeness of the problem statement, particularly regarding the charge's sign and the information provided.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem and expressing the need for clearer problem statements. Some guidance has been offered regarding the position of the charge and its velocity, but there is no explicit consensus on the approach to take.

Contextual Notes

There are concerns about missing information in the homework statement, particularly regarding the charge's sign and the clarity of the visual representation provided. Participants note that a more detailed problem statement would facilitate understanding.

guyvsdcsniper
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Homework Statement
What is the magnetic field at the position of the dot in the figure?
Relevant Equations
Cross Product
So when evaluation the cross product of the velocity of the charge and the unit vectors associated with the point I am getting

v x r = j x [ i + j].
Well j x j is 0.
j x i = -k, but yet the answer is positive. Why is this?

Screen Shot 2021-11-07 at 9.15.18 PM.png
 
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The vector r is the position of the point relative to the proton, not the position of the proton.
 
Why should there be a magnetic field? What is given in this problem that you did not include in the Homework Statement and is not shown in the picture you posted? We are not even told the sign of the charge.
 
kuruman said:
Why should there be a magnetic field? What is given in this problem that you did not include in the Homework Statement and is not shown in the picture you posted? We are not even told the sign of the charge.
The picture shows a proton at (1,1) with a given velocity and asks for the magnetic field at (-1,-1). It seems pretty clear to me.
 
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Orodruin said:
The picture shows a proton at (1,1) with a given velocity and asks for the magnetic field at (-1,-1). It seems pretty clear to me.
Yes, I see that now that I switched browsers.
 
kuruman said:
Yes, I see that now that I switched browsers.
Yes, I agree that we can figure out the problem which likely is to be solved.

However, I agree with your previous post in that a clear problem statement would be a great help. Especially one written as text and readable with any browser.
 

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