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Homework Help: Vector and partial derivatives

  1. Aug 27, 2008 #1
    1. The problem statement, all variables and given/known data

    Two charges one located at P at the position (x,y,z) and P' at the position (x',y',z')

    Let f= 1/R.
    Calculate Fx= partial derivative of f with respect to x.
    Calculate Fx'= partial derivative of f with respect to x'.

    There are sub question involving the same thing with other variables but if you could help me figure out the first part that should go easy.

    3. The attempt at a solution

    I solved R to be = (x-x')i + (y-y')j + (z-z')k... i think thats right but I do not know how to go about finding the partial derivatives of f. I have never really worked with vectors let alone inverse vectors with calculus.
  2. jcsd
  3. Aug 27, 2008 #2


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    There is no such thing as an 'inverse vector'. I would guess they mean R=|(x,y,z)-(x',y',z')|, Which is R=sqrt((x-x')^2+(y-y')^2+(z-z')^2).
  4. Aug 27, 2008 #3
    Right, I got that part. But what is a partial derivative of 1/ a vector?
  5. Aug 27, 2008 #4


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    It can't be a vector. 1/'a vector' doesn't make any sense. Are you sure they didn't write 1/|R|? It's just the partial derivative of a scalar function.
  6. Aug 27, 2008 #5
    Right *bangs head against the wall*. The only difference on the homework sheet between the vector and the magnitude is the vector is in bold. My stupid mistake.

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