Illustrations that I have added to Wikimedia Commons and inserted in some articles:
Illustration of the electric field surrounding a positive (red) and a negative (green) charge (click for larger image). I inserted this illustration in the Electric field article.
Illustration of the electric field surrounding two equal charges (click for larger image).
Illustration of the electric field surrounding one positive charge (click for larger image). I'm not quite satisfied with this one, but I don't see any article where it would be obvious to use, so I won't improve it just now.
There is a way to have Wikipedia loaded on your computer so that you can view it when you don't have access to the Internet. It's called XOWA, and it's compatible with Microsoft Windows, OSX, Linux and Android.
XOWA allows users to download and import their own copy of Wikipedia using official database dumps, or by special hosted database files specifically created for use within XOWA. The application is designed to accurately display Wikipedia content through its own built-in browser, or by an internal hosted web server which allows users to access content using a browser of their own choice.
XOWA can load and display multiple wikis. It is not limited to just Wikipedia.