Refractive index and total internal reflection

what is the refractive index of a material?

the speed of light in a vacuum divided by the speed of light in the material

the greater the refractive index…..

the more the light entering the material is refracted towards the normal

Snell’s law of refraction

n1 sin(angle of incidence)= n2 sin(angle of refraction)

what is the critical angle?

the critical angle is the angle of incidence required for the angle of refraction to be 90, so light refracts along the boundary between the two media

what is total internal reflection?

• when the light strikes the boundary at a large angle, it is totally internally reflected

• all the light is reflected back into the original medium

  • no light is refracted out of the original medium

what is the first condition for TIR?

the light must be travelling through a medium with a higher refractive index as it strikes the boundary with a medium with a lower refractive index (eg when light in glass meets air)

what is the second condition for TIR?

the angle at which the light strikes the boundary must be above the critical angle

the greater the refractive index……

the lower the critical angle