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How fast must the rotor of a generator rotate?

  1. Mar 18, 2009 #1
    1. The problem statement, all variables and given/known data
    The maximum indicued emf in a generator is 205rpm is 43.0V. How fast must the rotor of the generator rotate if it's to generate a maximum inducded emf of 55.0V?

    2. Relevant equations
    E= NBAsinwt

    3. The attempt at a solution
    205r/m*2 (Pi)/ 1rev81min/60s = 21.46rad/s
    magnet field isnt given, so how can u solve this?
     
  2. jcsd
  3. Mar 18, 2009 #2

    rl.bhat

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    Re: Ch20-11

    Check the formula for induced emf.
     
  4. Mar 18, 2009 #3
    Re: Ch20-11

    i did, but ur not given enough info to solve it, when u have E=-N ( magnetic flux)/ time or motion emf which is E= Blv
     
  5. Mar 18, 2009 #4

    rl.bhat

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    Re: Ch20-11

    Formula for induces emf is E = NBAwsin(wt)
     
  6. Mar 19, 2009 #5

    rl.bhat

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    Re: Ch20-11

    When a coil is moving in a magnetic field, E = -N( change in magnetic flux/time)
    When a conductor is moving a magnetic field with a velocity v, E = Blv.
    In your problem you hve to the first formula. At any instant th magnetic flux = NBA*cos(wt)
     
  7. Apr 1, 2009 #6
    Re: Ch20-11

    The eq for the induced emf is NBAwsin(wt). To max this eq out you have to realize the max value for the sin function is 1. Therefore, the max emf = NBAw. Since they give you what the max emf is for an w=205rev/min, you can simply solve for a value of (NBA). and use this same value for (NBA) in the eq 55V=(NBA)(w). You have to realize that the values for N, B, and A are not changing for this situation. You do not really have to change the w to SI units, or, 21.46 rad/sec. You can use the 205 rev/ min as the w to find a value for (NBA) and plug this into the eq 55V = (NBA)(w). Either way you get approx 262 rev/min.
     
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