State what is meant by the term refraction.

The diagram below shows a ray of light travelling from air into the flat face of the semicircular glass block.

Draw on this

Describe the positions of: (i) the angle of incidence, represented by ${\theta }_1$ in the diagram (ii) the angle of refraction, represented by ${\theta }_2$ in the diagram

State the equation linking the refractive index of the glass ($n$), the angle of incidence (${\theta }_1$), and the angle of refraction (${\theta }_2$).

Describe an experimental method to determine the refractive index of the glass block using a ray box, a protractor, and a sheet of paper. Your description should include:

• how to position the block and record the paths of the light rays,
• what specific measurements to take,
• how to obtain a reliable range of results,
• how to use a graph of your results to find the refractive index.