Describe the difference between reflection and refraction (assume the mediums have smooth surfaces)

Reflection: a wave hits a surface, and bounces back into the medium it was originaly in

Refraction: a wave enters a medium with a different refractive index to the original medium it was travelling in, at an angle different to the normal (90 degreees to surface). This changes the wave speed and wavelength, and therefore directon of the wave

The differences: in refraction the wave enters the medium, whilst in reflection the wave stays in the same medium. In reflection the wave properties stay the same, whilst the wave speed and wavelength change in refraction