Cross Product Confusion

  • #1
Hi all,

Just having some trouble understanding a certain example of cross product. It's actually for physics, but figured it belongs in this forum.

In the question I am supposed to cross (dl)y hat with (x1)x hat.

So I go (0 dl 0) x (x1 0 0) = (-x1dl)z hat. But turns out the answer the computer looking for is the same but without the negative. Wouldn't that be the case if i crossed it backwards, i.e. (x1)x hat cross (dl) y hat ??
 

Answers and Replies

  • #2
798
1
Yes,
[tex](0, dl, 0)\times{(}x_1, 0, 0)=-xdlk[/tex]
and
[tex](x_1, 0, 0)\times{(}0, dl, 0)=xdlk[/tex]
 
  • #3
Well then if that's the case I'm still confused. Because then my answer should be right.
 
  • #4
mathman
Science Advisor
7,898
461
You need to write the question exactly as it presented, since the cross product depends on which comes first.
 
  • #5
Ok, I am thinking that there is an error in the system, because according to the Biot Savart Law it has a dl x r in the numerator, where r = (x1 0 0) and dl = (0 dl 0). So I computed that but yet my answer was wrong.
 
  • #6
mathman
Science Advisor
7,898
461
Ok, I am thinking that there is an error in the system, because according to the Biot Savart Law it has a dl x r in the numerator, where r = (x1 0 0) and dl = (0 dl 0). So I computed that but yet my answer was wrong.
Check the computer program specs. Presumably it will tell you how it interprets a cross product for the order in which the vectors are input.
 

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