① Draw the light path diagram as shown in the figure. When the incident point is at point C, sini=OCR= 12, I = 30.

The refraction angle r = I+∠ d.

tan∠D=R2OD？ Rcos30 =33, then the solution is, ∠ d = 30.

So the refractive index is n=sinrsini=3.

(2) To make the spot on the desktop on the right side of point A disappear, the light should be totally reflected on the AB surface to increase the incident angle. According to the knowledge of geometry, the incident light should move upward.

Answer: ① The refractive index of glass is 3;

(2) To make the spot on the desktop on the right side of point A disappear, the incident light should move upward.