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The illustration displays a closed rectangular path a b c d of length delta l. The boundary divides the width of the rectangular path into two equal paths, start fraction delta h over 2 end fraction. The l caret sub 1 and the l caret sub 2 are the unit vectors along segments a b and c d respectively. The H sub 1 and the H sub 2 are the magnetic fields in the media 1 and 2 respectively. The n caret and the n caret sub 2 are the normal to the loop and to the surface of medium 2 respectively. The magnitude of the component of the surface current density normal to the loop is J sub s. The directions of the components H sub start expression 1 t end fraction and H sub start expression 2 t end fraction are parallel to the media. The directions of the components H sub start expression 1 n end fraction and H sub start expression 2 n end fraction are perpendicular to the media in the upward directions.