[填空题]
The diagram shows a light ray that travels from air into a glass block.
(1)State what is meant by the refractive index of a medium.
(2)Knowing that
The refractive index of glass = 1.5
The angle of incidence = $40^{\circ}C$
Draw on the diagram a ray to represent the path of light in the glass block.
(3)Calculate the angle of refraction inside the glass block.$θ_2$= $^{\circ}C$
2.Another light ray travels inside the glass block as shown in the diagram.$θ_c$= $^{\circ}C$
Determine the minimum angle $θ$ for which this reflection would occur.
