[单选题]
A ray of light is incident on a material made from three
zaft3b -(if9e-iuw4 p layer
zcli64;i5dl,y)2n sjjhq vjn v9* d8a xr/4wvs, each having a different optical density, so that in
6zd 5w*9lx q )j44vi2/d8, rlnjivsnj avy;cheach layer the light travels at a different speed.
- For layer 1: refractive index $=n_{1}$ and the speed of light $=c_{1}$
- For layer 2: refractive index $=n_{2}$ and the speed of light $=c_{2}$
- For layer 3: refractive index $=n_{3}$ and the speed of light $=c_{3}$
- Angle of incidence $=i$
- Angle of refraction $=r$
This is illustrated in the diagram below:
Which is the correct expression for $c_{3}$, the speed of light in the thirdlayer?