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

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1. Apr 14, 2017

### alexdr5398

1. The problem statement, all variables and given/known data

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. Apr 14, 2017

### 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?

3. Apr 14, 2017

### TSny

If the current increases, would anything else on the right side of the above equation change?

4. Apr 14, 2017

### alexdr5398

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?

5. Apr 14, 2017

### TSny

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.