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Homework Help: More review problems

  1. Mar 1, 2004 #1
    11) the diagram shows 3 equally spaced wires that are perpendicular to the page. the currents are equal, 2 being out of the page and 1 going into the page. rank the wires according to the magnetude of the forces on them, from least to greatest.


    . x .
    1 2 3

    12) A proton (charge e) traveling perpendicular to a mag field, experiences the same force as an alpha particle (charge 2e) which is also traveling perpendicular to the same field. the ratio of their speeds, v (proton) / v (alpha)

    My answer is 2

    13) the mag field in T a distance of 2 cm from a long straight wire carrying a current of 2 A is about

    15) 2 long parallel straight wires carry equal currents in opposite directions. At a point midway between the wires, the mag field they produce is?

    a) zero ( I picked a)
    b) non-zero and along a line connecting the wires
    c) non-zero and parallel to the wires
    d) non-zero and perpendicular to the plane of the two wires
    e) non of the above

    16) 2 long strait wires are parallel and carry current in the same direction. the currents are 8 A and 12 A and the wires are separated by .4 cm. the mag field in tesla at a point midway between teh wires is?

    18) the mag field outside a long straight current-carrying wire depends on the distance R from the wire axis according to
    a) R
    b) 1/R
    C) 1/R^2
    d) 1/R^3
    e) 1/R^3/2
     
  2. jcsd
  3. Mar 1, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Field from a current-carrying wire: Learn it!

    No. First note the symmetry between the left and right wires: they must experience the same force. Now find the B field that they exert on the middle wire.
    OK.
    Learn the expression for the field produced by a current carrying wire; look it up.
    No. Once again, you must know the field produced by a current-carrying wire. No calculation is needed here, but you do need to know what direction the field points. Compare with #11
    Same comment.
    Ditto.
     
  4. Mar 1, 2004 #3
    On #18

    B= uI/2pieR

    So the answer should be 1/R. Right?

    Nautica
     
  5. Mar 1, 2004 #4
    I am confused about this one.

    15) 2 long parallel straight wires carry equal currents in opposite directions. At a point midway between the wires, the mag field they produce is?

    a) zero
    b) non-zero and along a line connecting the wires
    c) non-zero and parallel to the wires
    d) non-zero and perpendicular to the plane of the two wires
    e) non of the above
     
  6. Mar 1, 2004 #5
    On #11 the 1,2,3 were the names of the wires. I forgot to include my answer

    2 would have the greatest and 1 and 3 would be tied. right?
     
  7. Mar 1, 2004 #6

    d
     
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