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Homework Help: Determining an electric field in vector form, got the answer, just checking.

  1. Jul 11, 2005 #1
    Hello everyone, I finally finished the chapter and now i'm going to attempt to do some problems. Well the first problem says: A surface has the are vector A = (2[itex]\hat i + 3\hat j[/itex]m^2. What is the flux of a uniform electric field through it if the field is (a) E = 4[itex]\hat iN/C[/itex] (b) [itex] E = 4\hat k[/itex]. The answer for (a) is 8 Nm^2/C (b) 0. The answer is 8 for the first one because well (4)(2)...the j component isn't used at all because why? Also b is 0 because k isn't in the same vector as i or j, is that right or am i getting lucky?
  2. jcsd
  3. Jul 12, 2005 #2
    There's no j component for a. because the j component of the field you're given is 0. You're taking a dot product to find the flux, ie

    [tex]\Phi_{E} = \vec{E} \cdot \vec{A}[/tex]

    So, when you evauluate that and you multiply the j components, you get 3 x 0 which is of course 0. That's the same reason that b. is 0, because [itex]\vec{A}[/itex] has no k component and [itex]\vec{E}[/itex] has no i or j components.
  4. Jul 12, 2005 #3
    ohh!! i forgot all about that, i have to refresh on vector math! thanks!
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