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Homework Help: How large is the voltage generated?

  1. Apr 2, 2009 #1
    1. The problem statement, all variables and given/known data
    A Boulder farmer, frustrated by his monthly electricity bill, decides to power his extra-
    large-screen television set by using a home-built generator. He knows that the Earth
    acts like a huge magnet and wants to make use of this magnetic field to generate an
    electromotive force (voltage difference) for his TV. The generator is made up of two
    large conductors coming out of the house, connected to a large sliding (conducting)
    rail pulled by his two horses, as shown in the diagram on the left below. In Boulder
    the angle of the Earth’s magnetic field, which is pointing into the ground, with the
    horizontal (ground) is 66o (see diagram on the right below) and the magnitude of the
    field is 53 µT (micro T). The TV acts effectively like a 4 Ω resistor in the circuit, and
    the friction between the moving parts is negligible.
    Length of the slide is 15 m and a width of 25 m.

    The horses can pull the sliding rail with 8 miles per hour. How large is the
    voltage generated across the leads to the TV?

    2. Relevant equations

    so it would be EMF = bcos(theta)*voltage*length

    3. The attempt at a solution
    well i got an answer of like .001 V and that just doesnt seem right but i dont really know, just wanted to check
  2. jcsd
  3. Apr 2, 2009 #2
    sorry got a little more with this. so i found the Magnetic force to be 3.03x10^-23 which again doesnt seem right. i did Fmag=q(v*B) so 1.6*10^-19(3.58x.000058T) So then i need to find the work done which would just be the Force x velocity but i got my work as something very low so again i just dont know if that makes sense.
  4. Apr 2, 2009 #3


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    Staff Emeritus
    Science Advisor
    Homework Helper

    That doesn't look right. The correct formula for EMF involves area ...
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