[" An observer can see through a pinhole,the top "],[" end of a thin rod of height h,placed as shown in "],[" the figure.The beaker height is "3h" and its radius "],[" is h.When the beaker is filled with a liquid up to "],[" a height "2h," he can see the lower end of the rod."],[" Theight "2h" ,he can see the lower end of the rod."],[" Then the refractive index of the liquid is "],[" Then the refractive index of the liquid is "],[qquad [pi,0],[3n,1]],[,=(n^(2)+n)/(2n)]