Question 5.13: Consider an interface between free space and an iron metal w......

Consider an interface between free space and an iron metal with \mu = 1000\mu _{o}. In free space, \pmb{B}_{1} makes an angle of \theta _{1} = 1.0^{\circ } with the normal to the interface.

Find (a) direction of \pmb{B}_{2} in the iron metal, and (b) ratio \pmb{B}_{2}/ \pmb{B}_{1}.

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(a) From the boundary conditions for H and B, we get

\frac{1}{\mu } B_{2t} =  \frac{1}{\mu_{o} } B_{1}\sin (1^{\circ })                                    (tangential  component  of  \pmb{H})                                    (5-97a) \\ B_{2n} =  B_{1}\cos (1^{\circ })                                                 (normal  component  of   \pmb{B})                                     (5-97b)

In the iron metal, we have
\tan \theta _{2} = \frac{B_{2t}}{B_{2n} } = \frac{(\mu /\mu_{o} ) B_{1}\sin (1^{\circ })} {B_{1}\cos (1^{\circ })} = 17.46 \\ Thus,   \theta _{2} =86.7^{\circ }

(b) Combining Eqs. (5-97a) and (5-97b), we obtain

B_{2} =\sqrt{ (B_{2t})^{2} + (B_{2n} )^{2}} = B_{1}\sqrt {(1000\mu_{o} /\mu_{o} )^{2} \sin^{2} (1^{\circ }) + \cos^{2} (1^{\circ })} \\ Thus,    B_{2}/B_{1} =17.5

 

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