Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Voltage and Electric field

  1. Sep 30, 2012 #1
    Here is the problem:

    Given that electric potential is given as a function of x and y: V(x,y)=20x4 + 60y3

    What is Ex at (2,1)?

    I have tried using E=-DV/DV, but I keep getting confused on how to derive this as it's been a while since I took calculus. I am also unsure of how to plug in the number, like if I only derive the x component and only plug the x into it, or if the y component is involved.
     
  2. jcsd
  3. Sep 30, 2012 #2
    Use the -gradient.
     
  4. Sep 30, 2012 #3
    And how would I do that?
     
  5. Sep 30, 2012 #4
    What's the formula for finding the gradient of a function in rectangular coordinates?
     
  6. Oct 1, 2012 #5
    If using the gradient, just take the partial derivatives. One with respect to x, the other with respect to y.

    If I understand the question right, you want to just take the partial derivative with respect to x to get Ex. That's 80x^3. The y term completely disappears.

    In this particular example when you take the partial with respect to x, all of the y terms disappear. That doesn't always happen. So all you would have is plug in the 2 for x.
     
    Last edited: Oct 1, 2012
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook