Answers for Practice Test #3

  1. (a) In order to find the force on q1 you need the direction of the magnetic field B2 due to charge q2. RHR shows that B2 is OUT of the page at the location of q1. So, if v1 is up and B2 is out, then F2on1 is to the RIGHT.
    B2 = 1.05e-5 T and F2on1 = 0.0288 N.
  2. (a) current in the long straight wire is INTO the page
    (b) Iwire = 46 A.
  3. I = 9A into
  4. (a) B if OUT of the page
    (b) 5 is positive (force in same direction as 4), 1 and 2 are negative (force is in opposite direction as 4), and 3 is neutral (no force)
    (c) q1 > q2
    (d) m5 < m4
  5. I = 115A
  6. ds points in direction of current, rhat points from source (current segment) towards test location (point P) and theta is the angle between ds and rhat.
  7. magnetic force is directed down, so positive charges collect at bottom. induced potential (motional emf) is 1.2V and electric field E = dV/dx = 1.85 V/m directed UP.
  8. using the 4-step question process, only a and c would produce a counter-clockwise current