1. Not finding help here? Sign up for a free 30min 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!

Flux Problem

  1. Oct 4, 2014 #1
    1. The problem statement, all variables and given/known data

    A 1x1x1 cm box with edges aligned in the xyz-axes is in the electric field E = (350x + 150)i N/C, where x is in meters. What is the net electric flux through the box?

    2. Relevant equations

    flux = ExAx + EyAy + EzAz

    3. The attempt at a solution

    I substituted into the formula above, including 0.01m for x. I get:

    flux = [(350*0.01 + 150)(0.01)^2] + 0 + 0 = 0.01535 Nm^2/C

    I then multiply by two because the field is coming through the back and front of the box. I'm not getting the answer right though. What am I missing?
     
  2. jcsd
  3. Oct 4, 2014 #2

    Doc Al

    User Avatar

    Staff: Mentor

    You cannot just multiply by 2. Calculate the flux through the front and back sides. (They aren't the same.) Then add to get the net flux, being careful with signs.
     
  4. Oct 4, 2014 #3
    Why aren't they the same? Isn't it a cube? Maybe I don't understand the expression (350x + 150)i like I think I do.

    Does the expression mean 350x on the way in and 150 on the way out?
     
  5. Oct 4, 2014 #4

    Doc Al

    User Avatar

    Staff: Mentor

    What's the field at x = 0? (Where one side is.) At x = 0.01? (Where the other side is.)
     
  6. Oct 4, 2014 #5
    I'm still lost. The field at x=0? There are an infinite number of points on x=0, depending on y and z, no? Same at x=0.01.

    I mean, the answer is 3.5x10^-4, according to my text. I substituted 0.01m into the expression and multiplied by (0.01)^2. Don't have a clue why though. What happened to the 150?
     
  7. Oct 4, 2014 #6

    Doc Al

    User Avatar

    Staff: Mentor

    The field only depends on x. So all points with the same x value have the same field.
     
  8. Oct 4, 2014 #7
    So what does the 150 mean? Does it have anything to do with the problem?
     
  9. Oct 4, 2014 #8

    Doc Al

    User Avatar

    Staff: Mentor

    Of course it does! 350x + 150 is a function that gives you the magnitude of the electric field at any point. You can't leave out the 150.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Flux Problem
  1. Flux problem (Replies: 2)

  2. Flux problem (Replies: 1)

  3. Electric flux problem (Replies: 7)

  4. Magnetic flux problem (Replies: 25)

Loading...