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# N=300 turns of this wire are uniformly wound on a permanent magnet shaped as a cylinder whose length is equal to l=15 cm. When a current I=3.0 A was passed through the wiring the field outside the magnet disappeared. Find the coercive force Hc of the material from which the magnet was manufactured.

Solution
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#### The coercive force Hc is just the magnetic field within the cylinder. This is by circulation theorem, Hc=NIl=6kA/m(from ∮→H⋅d→r=I, total current, considering a rectangular contour.)

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