My assumption is that it is an error that has just propagated from one part of the e-book into that section when the files were created (somewhere in the e-book that diagram is used in its correct context!). I will request that it be moved.I'll second that. The description of a parallel plate capacitor in that context seems 'quaint' to say the least. Better would be some pictures to highlight the vocabulary which was just introduced. Pictures are worth many words.