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Homework Help: EMF generated by a magnetic field

  1. Nov 10, 2012 #1
    1. The problem statement, all variables and given/known data
    An automobile with a vertical radio antenna of length 75 cm travels at 80 km/h eastward. The Earth’s magnetic field has magnitude of 7x10-5 T and is directed 52o downward with respect to due North. What EMF is generated between two ends of the antenna? Comment on the polarity of EMF as well.

    2. Relevant equations
    ε = Blv
    To find V in m/s: 80km/h X 1000m/km X 1h/60m X 1m/60s = 22.22 m/s
    l = 0.75m
    θ = 52°

    3. The attempt at a solution
    7x10-5 X .75 X 22.22 X sin(52°)

    = 9.1925 X 10-4 V

    That make sense to you guys for part A?

    As for Part B, the polarity, I don't really know how to determine. I know I will have to factor the direction of the car being towards the east, and the direction of the magnetic field, but I do not understand how one will interact with the other. Any hint in the right direction would be appreciated for this part!
  2. jcsd
  3. Nov 10, 2012 #2
    Yes, that looks good. In my opinion you should mention which equation you are using and use SI symbols in the equation. And as for polarity, use left-hand rule to determine which end becomes negatively charged.
  4. Nov 10, 2012 #3
    I always use units in the assignment, it just gets confusing on the computer :D

    And isn't it the right-hand rule for everything related to magnetic fields?
  5. Nov 10, 2012 #4
    No, the left-hand rule is for negatively charged particles.
  6. Nov 10, 2012 #5
    Ahh I see, and since it's going downwards, then its negatively charged, is that correct?
  7. Nov 12, 2012 #6
    If I use the left-hand rule, I am deducing that the top of the antenna would be negative and the bottom would be positive, would that be correct?
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