A ray of light falls at right angles on one of the short faces of a glass prism whose cross-section is a right-angled isosceles triangle, as shown in the figure. It goes straight in and meets the long face (the hypotenuse) inside the glass. The smallest refractive index of the glass for which the ray is totally reflected at the hypotenuse is closest to

Fig. 1: A right-angled isosceles glass prism. A ray enters one short face at right angles, meets the long face at 45 degrees and is reflected out through the other short face.