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The interface is shown between medium 1 with permittivity epsilon 1 and medium 2 with permittivity epsilon 2. In medium 1, E sub 1 is the electric field between E sub 1 n and E sub 1 t. In medium 2, E sub 2 joins the E sub 2 n and E sub 2 t. The rectangular loop a b c d a is labeled with l caret sub 1 and l caret sub 2. c d is labeled delta l. a d divided into two for medium 1 and medium 2 is labeled with start fraction delta h over 2 end fraction in both the mediums. Similarly, a cylinder is labeled with density sub 1 n in medium 1 and density sub 2 n in medium 2. Vector n sub 2 is labeled in medium 1 and vector n sub 1 is labeled in medium 2. The height of the cylinder is labeled, start fraction delta h over 2 end fraction in both the mediums. The center part of the cylinder is labeled, rho sub s.