How does diffraction differ from refraction?
Refraction is the bending of waves when it passes from one medium to another.
Eg. when light (waves) passes from air to water, (could be experimentally proved with the aid of a pencil inside a glass of water). The light waves (the pencil) will appear to be bent from it's original shape. The speed and direction of the wave are mainly affected.
Diffraction is a complex phenomena that occurs when waves passes through a gap or as termed in experiments; slits. Many factors of the wave change when diffraction occurs. The amplitude and sometimes the frequency of the wave are affected.