MYP Physics sample question: Refraction and total internal reflection

A ray of light travels from air into a rectangular glass block, and later a ray inside the glass hits the glass–air boundary at a large angle.

1. (a)State what is meant by refraction.[1]
   Show the mark scheme for (a)

   • • The change in direction of a wave when it passes from one medium into another, caused by a change in speed (1)
2. (b)Explain why a ray of light bends towards the normal when it enters the glass.[2]
   Show the mark scheme for (b)

   • • Light travels more slowly in glass than in air (1)
   • • so the ray bends towards the normal as it enters the denser medium (1)
3. (c)State two conditions needed for total internal reflection to occur at the glass–air boundary.[2]
   Show the mark scheme for (c)

   • • The light must be travelling from the denser medium (glass) towards the less dense one (air) (1)
   • • The angle of incidence must be greater than the critical angle (1)

Always connect bending to a change in speed. Optical fibres work because of total internal reflection, which is a good example to quote.