For an interface with the free charge density rom(DnI -Dn2)=af we have D1 cos 8 COS 02=0. Erico el cos 1= Er2eo e2 cos 82 From the tangential component Et1= Et2, we have 1 sIn 01=Bo sin 02 Combining these two equations yields tan tan The medium with the larger relative permittivity Er has a larger angle 0 from the normal