Vector evaluation & Lorentz force law

  • Thread starter Roodles01
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  • #1
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Homework Statement


An electron in a magnetic field B=2.0T(ex-ez) has velocity v=(2.5x107 ms-1 (ex-ey)
a) calculate magnetic force on electron at that instant
b) what is the magnitude of this force



Homework Equations


I am using the Lorentz force law.
F = q(vXB)
& evaluating the directions by vector

My argument is that the ey term is negative, but another person evaluates this as positive. Please confirm whether I'm right or wrong.

This affects the outcome of magnitude of force, too.

The Attempt at a Solution


F = -e 2(2.5x107) (ex-ez)* (ex-ey)

I ex ey ez I
I 1 . -1 . 0 I
I 1 . 0 . -1 I

= ex((-1x-1)-(0x0)) + ey((1X-1)-(0x1)) + ez ((1x0)-(-1x1))
= ex - ey + ez)

so
F = -8x10-12 (ex - ey + ez)
 

Answers and Replies

  • #2
rude man
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Better believe your friend about the sign of the j term! (Re-check your determinant).
 
Last edited:
  • #3
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Ah! Having looked at it, I found that I didn't change the sign for the second term.
So simple it's annoying.
Thank you.
 
  • #4
rude man
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Ah! Having looked at it, I found that I didn't change the sign for the second term.
So simple it's annoying.

Welcome to the club! :smile:
 

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