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

Choose the two correct statements:

• sound waves are transverse waves
• when light travels from air into glass, its speed increases
• the virtual image formed by a plane mirror is the same distance behind the mirror as the object is in front of it
• waves transfer matter from one place to another
• the angle of refraction is measured between the refracted ray and the normal

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.