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Homework Help: Okay, I am down to only a few.

  1. Mar 1, 2004 #1
    I feel pretty confident in the rest of the problems and am down to these. I appreciate the help.

    16) 2 long straight wires are parallel and carry current in the same direction. the currents are 8 A and 12 A and seperated by 0.4 cm. The mag field in tesla at a point midway between the wires is?

    I used B=uI/2(pie)r but did not come up with the right answer.

    20) a uniform magnetic field is directed into the page. A charged particle, moving in the plane of the page, follows a clockwise spiral of decreasiing readius. An explanation would be.

    My answer is: the charge is poistive and slowing down

    21) electrons are going around a circle in a counterclockwise direction. At the center of the circle they produce a magnetic field that is:

    My answer: out of the page

    24) 2 parrallel wires, 4 cm apart, carry currents of 2 A and 4 A respectively, in opposite directions. The force per unit length on of one wire on the other is:

    4 x 10^-5 attractive

    26) Units of magnetic field might be:

    a) C m/s
    b) C s/m
    c) C/kg
    d)kg/C s
    e) N/C m

    23) The units of motional emf are:

    a) volt/second
    b) volt meter/second
    c) volt/tesla
    d) tesla/second
    e) tesla meter^2/second

    I dont have a clue on 23 or 26

  2. jcsd
  3. Mar 1, 2004 #2
    for P16 u need to consider directions as well it would be difference of the 2

    i.e {uI1-uI2}/2 r
    Last edited: Mar 1, 2004
  4. Mar 1, 2004 #3
    If I subtract the 12 - 8 I get 4 so

    (4pi x 10^-7) x 8 / 2pi x .004 = 2 x 10^-4

    this is not a choice, these are the choices

    a) 0
    b) 4 x 10^-4
    c) 8 x 10^-4
    d) 12 x 10^-4
    e) 20 x 10^-4
  5. Mar 1, 2004 #4
    Note concerning units

    U know various formula now look for pro 26

    what does option a represents charge*velocity but there is no such formula for magnetic field which corresponds to it

    Now for option e Force/{charge*length} which correspond to formula


    for pro 23

    emf = BdA/dt= T*m^2/s
  6. Mar 1, 2004 #5
    u are doing calculation error it should be 16/4=4*10^-4
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