Refraction and Total Internal Reflection

Refraction

Refraction is the bending of a wave, like light, as it passes from one medium to another where the speed of the wave changes

Draw a diagram for refraction and reflection

Refraction

Refraction is the bending of a wave, like light, as it passes from one medium to another where the speed of the wave changes

Draw a diagram for refraction and reflection

What is the refractive index of a material

The ratio of sini/sinr

Snell’s Law

What is the refractive index of light in space and air?

1

What happens to the velocity, frequency and wavelength of an EM wave as it travels from an optically less dense to an optically more dense medium?

• Velocity: decreases

• Frequency: unchanged

• Wavelength: decreases

Total internal reflection

Total internal reflection (TIR) is a phenomenon where light traveling from a denser medium (like glass or water) to a less dense medium (like air) is completely reflected back into the denser medium instead of being refracted.

What conditions are required for total internal reflection to take place?

• The incident substance has a larger refractive index than the other substance

• The angle of incidence exceeds the critical angle

What happens when the critical angle = the angle of incidence?

A refracted ray at 90°

Total internal reflection diagram

Fibre optics diagram

Refractive index between the cladding and core

The cladding has a lower refractive index than the core

What does the cladding do?

The cladding protects the core from damage while assisting total internal reflection

Why must the core be narrow?

To prevent multipath dispersion, where multiple light rays catch up with each other

An optical fibre consists of a core, cladding and an outer sheath. State the purpose of the outer sheath in an optical fibre

Prevents damage to the fibre

Explain why optical fibres used for communications need to have cladding

• Keeps signal secure

• Maintains quality

• It keeps light rays in (due to internal reflection)