http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/waves/
http://revise-physics.net/IGCSE/pdf/P9Waves.pdf
http://www.gcse.com/waves.htm
http://www.physicsclassroom.com/Class/waves/
http://library.thinkquest.org/10796/
Copy – paste the above links on address bar to study waves in detail