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Okay, this is question 2830.
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We have two long parallel wires that are separated by a distance of 2 .5 centimeters.
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I've written that over here and converted the distance to meters.
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And the force per unit length that each wire exerts on the other is 4 times 10 to the 5 newton.
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So it's going to be f over l.
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We're given that here.
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And we're told the current in one of the wires, but we're asked to find the current in the second wire.
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So here's the expression for the force per length from two different wires with different currents, i1 and i2.
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So we have i1 here.
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We have f per l.
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We also have r.
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So all we have to do here is rearrange this equation.
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So we can solve it for i2.
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And that will give us the magnitude of i2.
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Since we have everything else, we can plug in here.
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So when we rearrange this, we're going to need to multiply a factor of 2 pi r over here times f on the left...