Refraction of Waves

Question 1

Why does refraction occur?

Answer 1

When light travels through a denser medium its speed decreases so it bends towards the normal as its wavelength decreases, whereas in a less dense material it bends away from the medium because it speeds up.

Question 2

What is the refractive index?

Answer 2

It indicates the amount of deviation - the greater the deviation, the higher the refractive index.

index = speed in vacuum/speed in medium

Question 3

Why does dispersion occur?

Answer 3

Each colour slows down by a different amount when white light enters a denser medium and speeds up by a different amount when light leaves the medium. The different colours have different refractive indices so they have a different angle of refraction.

Question 4

What is Snell’s law?

Answer 4

index = sin angle I / sin angle r

Question 5

What happens to the angles when light goes from dense to less dense?

Answer 5

The angle of refraction is larger than the angle of incidence.

Question 6

When does TIR happen?

Answer 6

When light travels from one medium towards another with a lower refractive index so that the angle of refraction reaches 90* as the angle of incidence increases

• The angle of incidence exceeds the critical angle

Question 7

What decreases the critical angle?

Answer 7

The denser then material, the high the refractive index and the lower the critical angle.