In this video the wave phenomena of reflection and refraction are explored using two online applications from the excellent PHET project at the University of Colorado, USA (http://phet.colorado.edu/). The reflections of a wave on a string when the end is fixed are compared with that when the end is free to move. Refraction is defined and Snell's law is introduced. This video will support your learning in IB Physics topic 4: Oscillations and waves (WAV).
The sound quality is not great in this video so many apologies for that but I hope you can bear with it - I am sure you will find the lesson useful.