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Homework Help: Magnetic field of earth on airplane

  1. Mar 24, 2009 #1
    1. The problem statement, all variables and given/known data
    This isn't a homework problem with variables and numbers; it is a concept question:
    An airplane is flying west in level flight over Massachusetts, where the Earth’s magnetic field is directed downward below the horizontal in a northerly direction. As a result of the magnetic force on the free electrons in its wings, one of the wingtips will have more electrons than the other. Which one (north or south wing) is it? Will the answer be different if the plane is flying east?

    2. Relevant equations
    I'm not sure if this is just a common sense question, where the north wing would have more electrons than the south wing due to the earth's magnetic field? And if that what the case, would it not be different if the plane flew east?

    3. The attempt at a solution
  2. jcsd
  3. Mar 24, 2009 #2


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    Homework Helper

    Hi Brit412,

    It seems to me that you are saying that the north wing will have more electrons because the magnetic field has a northwards components, and if so that reasoning is not correct.

    One wing will have more electrons because the electrons feel a force moving them toward one of the wings. How can you determine the direction of the magnetic force on the electrons in this problem?
  4. Mar 24, 2009 #3


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    The downward component B of the field is perpendicular to the wings and the velocity, so potential V = L*v*B will be induced from wingtip to wingtip (distance L). Hold your left (for negative charges) hand so the fingers are down (magnetic field), thumb pointing west (velocity). Your palm pushes to the north, indicating that electrons will be pushed that way. There are more electrons on the north side than the south. Flying east would reverse the effect because your hand would have to be turned so the thumb points east.
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