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

Select the two correct statements:

• sound waves can travel through a vacuum
• when light travels from air into glass, its wavelength decreases
• the angle of incidence is measured between the incident ray and the boundary surface
• the critical angle is the angle of incidence for which the angle of refraction is $90^{\circ }$
• electromagnetic waves are longitudinal waves

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

Draw on this

Use the diagram to: Find the angle of incidence, $i$.

Use the diagram to: Find the angle of refraction, $r$.

State the formula linking refractive index ($n$), angle of incidence ($i$), and angle of refraction ($r$).

Calculate the refractive index, $n$, of the glass block. Give your answer to 3 significant figures.

Describe an experiment to determine the refractive index of a rectangular glass 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.