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Cartesian coordinates vectors

  • #1

Homework Statement


upload_2017-2-10_15-9-0.png


Homework Equations




The Attempt at a Solution


upload_2017-2-10_15-10-26.png


the answer given is the same but without the negative sign, I don't understand because the crossproduct of unit vectors
upload_2017-2-10_15-13-41.png

when using a Cartesian coordinates of the directions given by the right-hand rule? Is the positive z direction pointing out of the page if X and Y are as follows
upload_2017-2-10_15-18-3.png

apologies if this is in the wrong section, thanks for any help in advance
 

Answers and Replies

  • #2
BvU
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Yes. ##\hat {k} = \hat {\bf \imath } \times\hat {\bf \jmath}## , so z points towards you, out of the screen.

Corkscrew rule I call it. Turn ##\hat{\bf \imath }## over the smallest angle towards ##\hat {k}##. Corkscrew will go in the minus y direction : $$\hat \imath \times\hat k = -\hat \jmath $$
 
  • #3
TSny
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The problem doesn't specify which of the two wires the charge -q is a distance b from. Does the answer change if you pick the other wire to be a distance b from -q?
 
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  • #4
Thank you both your answers, TSny I thought the same, closer to the top wire the combined magnetic field would be in the opposite direction . Maybe the question is just not very good
 

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