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What happens to a coil of wire as current is increased?

  1. Apr 14, 2017 #1
    1. The problem statement, all variables and given/known data
    3jFKimM.jpg

    2. Relevant equations
    L = (N * F_b) / I (where F_b is the magnetic flux)
    emf = -L * (dI/dt)

    3. The attempt at a solution
    I originally thought that the inductance would decrease since it is inversely proportional to current. But, looking at the equation for emf, that would also mean that emf would decrease since L is decreasing and dI/dt is constant.
     
  2. jcsd
  3. Apr 14, 2017 #2

    berkeman

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    Staff: Mentor

    Your answer looks correct to me. The EMF is constant since the increase in I is linear. The inductance is a physical quantity, not affected by current (for an air core inductor). If the inductor had a ferrite or iron core, would that change your answer? :smile:
     
  4. Apr 14, 2017 #3

    TSny

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    Homework Helper
    Gold Member

    If the current increases, would anything else on the right side of the above equation change?
     
  5. Apr 14, 2017 #4
    Oh, so the flux is increased by the increase in current which counters the current in the denominator?

    And since inductance is a physical quantity, it can never be changed by the properties in a circuit?
     
  6. Apr 14, 2017 #5

    TSny

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    Gold Member

    Yes. If the current doubles, then the flux doubles. So, the formula would leave L unchanged.

    Yes. The inductance is determined by the physical properties of the inductor (size, shape, number of wraps, type of core, etc.) as berkeman pointed out.
     
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