A capillary tube made of a material of refractive index 2. The outer radius of the tube is $\sqrt{3}R$  and inner radius is R. The tube is filled with a liquid of refractive index 1.5 A light ray is incident on the tube at grazing incidence (angle of incidence approximately $\approx {90}^0$ ) on the outer surface of capillary tube as shown in the fig. The net angle of deviation is $k^0$  . Find the value of ‘$k$’