Unpolarised light is incident on the boundary between two dielectric media, whose dielectric constants are 2.8 (medium −1 ) and 6.8 (medium −2 ), respectively. To satisfy the condition, so that the reflected and refracted rays are perpendicular to each other, the angle of incidence should be $ tan^{−1}(1+\frac{10}\theta )^{\frac{1} 2}$, then the value of 𝜃 is _______.
(Given for dielectric media, $ \mu_r=1$ )