## Sentence Examples

**Hence****if****dS****and****dS**'**are****the****areas****of****the****ends**,**and**+**E****and**-**E**'**the****oppositely****directed****electric****forces****at****the****ends****of****the****tube**,**the****surface****integral****of****normal****force****on****the****flux****over****the****tube****is****EdS**-**E'dS**' (20),**and****this****by****the****theorem****already****given****is****equal****to****zero**,**since****the****tube****includes****no****electricity**.