A student makes several statements about light and sound waves. Only two of these statements are correct.

Choose the two correct statements:

• sound waves are transverse waves
• light waves are transverse waves
• the angle of reflection is always equal to the angle of incidence
• electromagnetic waves require a physical medium to travel through
• mechanical waves can travel through a vacuum

The diagram shows a ray of light travelling from air into a rectangular plastic block.

Draw on this

Use the diagram to: (i) Find the angle of incidence, $i$. (ii) Find the angle of refraction, $r$.

(i) State the formula linking refractive index ($n$), angle of incidence ($i$), and angle of refraction ($r$). (ii) Calculate the refractive index, $n$, of the plastic block. Give your answer to 3 significant figures.

Describe an experiment to determine the refractive index of a rectangular plastic block. In your answer, you should refer to:

• the apparatus that should be used
• the measurements that should be taken
• how the data should be analysed to find the refractive index.