1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Flux - simple integral computation

  1. Oct 6, 2009 #1
    1. The problem statement, all variables and given/known data
    A surface has the area vector A = 2i + 3j. What is the flux of a uniform electric field through it if the field is E = 4i?

    2. Relevant equations
    Integral calculus, vectors

    3. The attempt at a solution
    I don't understand why one could do this. The integral is of E and dA, not E and A. How can I use A to determine dA?

    This is a crackpot way I thought of

    [tex] \Phi = \int \vec{E} \cdot \vec{dA} [/tex]

    \Phi = \vec{E} \cdot \int \vec{dA}

    \Phi = \vec{E} \cdot \vec{A}

    Then Phi = 4i dot (2i + 3j) = 8 flux units

    This seems like wild fantasy though as I don't know if I can pull out a constant from a dot product integral
  2. jcsd
  3. Oct 6, 2009 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    There is no dA to speak of. You are given A which is the same everywhere and E which is uniform. Just take the dot product as you have in your third equation. There isn't much to this problem/
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook