An equilateral glass prism kept on a table has refractive index $\mu =\sqrt{2}$ . The prism is  illuminated by a narrow laser beam of power $p_0$  and the wavelength  $\lambda$ such that  refracted beam inside the prism is parallel to the base of prism. The change in weight  of the prism due to the incident laser beam is  $\frac{n\sqrt{2}{P}_0}{C}$ [C is speed of light] Find n.