A useful link relating to Elasticity of Supply http://www.bbc.co.uk/news/world-europe-44134010
And see below, where to find it in the spec:-
Edexcel spec reference 1.2.5 Elasticity of supply                                
AQA spec reference 4.1.3.4  Price elasticity of supply 
OCR spec reference P9 Explain, with the aid of a diagram, the different values of PES
https://www.apt-initiatives.com/