Source: http://web.a9lame.com/Documents/Lyc%C3%A9e/Bac%20FR/b-1er%20Bac%20International/a-1er%20Bac%20Sciences%20Math%C3%A9matiques/b-Physique/b-Semestre%20II/c-Le%20champ%20magn%C3%A9tique/a-Cours/Cours%203%20Le%20champ%20magn%C3%A9tique.pdf