Question

Total internal reflection only occurs when the second medium _____.

is air

has an index of refraction less than the first medium

has an index of refraction greater than the first medium

None of the above

first

medium

None of the above

Answer 1

Total internal reflection only occurs when the second medium - has an index of refraction less than the first medium.

Explanatioin: when a ray of light strikes the surface of two materials, 3 possible incident can happen.

a) A part of light croses the boundery and is refracted and other part reflect back from the surface. The angle of refraction is depends on the refractive index of the 2nd medium (refracted medium), and we can calculate from Snell's Law of refraction.

b) now when the refractive index of 2nd medium is less than the refractive index of 1st medium (incident medium) the refrctive angle is wider than 1st medium. If incident angle increases then acgle of refraction is also increases and the largest value of the angle of refraction can be 90. That is for which incident angle the the angle of refraction is maximum (90) is called Critical Angle.

c) Now when the incident angle is greater than the critical angle the light reflected back totally which is called Total Internal reflection.

So, total internal reflection occurs when the 2nd medium has refractive index less than the 1st medium.