Source: http://web.a9lame.com/Documents/Lyc%C3%A9e/Bac%20FR/b-1er%20Bac%20International/a-1er%20Bac%20Sciences%20Math%C3%A9matiques/c-Chimie/a-Semestre%20I/e-La%20conductance%20et%20la%20conductivit%C3%A9/d-Exercices/Exercices%204%20La%20conductance%20et%20la%20conductivit%C3%A9%20non%20corrige.pdf