55. Assume that a plane wave in air with an electric field \(\overrightarrow E =10\cos(\omega t-3x-\sqrt{3z})\widehat a_y\) V/m is incident on a non-magnetic dielectric slab of relative permittivity 3 which covers the region.    Z > 0 The angle of transmission in the dielectric slab is _________________ degrees.

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