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Homework Help: Flux above a flat horizontal surface

  1. Sep 17, 2014 #1
    So my question is, am I missing any key thing in answering the question below?

    Question: An electric flux of 149 N.m2/C passes through a flat horizontal surface that has an area of 0.67 m2. The flux is due to a uniform electric field. What is the magnitude of the electric field if the field points 15degrees above the horizontal?

    So I've tried E=I/(Acos(90-θ)
    I=flux, and A= area, 0.67

    E= 149/(0.67cos75)

    And I have gotten...

    =859.24 (this seemed too large)

    =204.98 (I didn't use parenthesis, and too low)

    =57.55 (this was just an odd one my calculator gave me)

    So, I believe that it should fall somewhere in the 400-650ish range but please help, I have no idea of what to do with my calculator's answers
  2. jcsd
  3. Sep 21, 2014 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    ... what leads you to that belief?

    If the angle is 0, then E=I/A = 222.39N/C - which would be a minimum, right?
    As the angle gets shallower, then you need a bigger E field to get the same flux.

    Your belief is that 15deg should give you 2-3 times the minimum field required for the flux?
    What is ##1/\sin(15^\circ)## ? You don't have to trust your calculator if you don't want to - figure the trig by hand.
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