Looking something to be charged?
Some teachers can illustrate things simply better :-) There are two illustrations reposted on @collectionoffirst Instagram and one from other sources. There more online puns especially on Pinterest for your curious learners. Make your class interesting and fun.
Secondly, someone illustrates it in another form.
Source:
http://images.slideplayer.com/7/1650454/slides/slide_75.jpg