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Homework Help: Simple questions on electric fields

  1. Jun 5, 2012 #1
    (1)Which of the following statements about electric field lines is false?

    a) They are perpendicular to the surface of an isolated conductor
    b) They never intersect
    c) They indicate the path along which a test charge moves
    d) More indicate a stronger field
    e) They can be either straight or curved
    f) They indicate the force on a test charge

    I have no idea how to answer this
    because they all seem to be true!!

    (2) The electric field strength at point P which is 30cm to the right of a point charge Q=-3.0x10^(-6)C is:

    a) 1.3x10^5 N/C
    b) 9.0x10^4 N/C
    c) 3.0x10^5 N/C
    d) 5.5x10^5 N/C

    I know the answer to this one is (c) however, why is it positive?? when I calculate the electric field I use E=k0 x Q/(r^2) and it is a negative answer -3.0x10^5 N/C.

    (3) For the previous question, the field at this point, points:

    a) towards the charge Q
    b) away from the charge Q
    c) up
    d) down

    If you can help me understand the answers and why that would be useful, I can't get my head around electric fields for some reason
  2. jcsd
  3. Jun 5, 2012 #2


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    Staff Emeritus
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    Give your justification for each one being true.
    They're only asking for the electric field strength which is the magnitude of the field, not the direction.
    For (3); In what direction would the force be on a positive charge, placed at this point?
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