Posted by Lizzie on Sunday, December 28, 2008 at 1:35pm.
With regard to how to know if the ebonite rod acquires a positive or negative charge, you have to do the experiment to find out, and compare the result with other materials that are defined to have a particular charge.
The tradition that electrons are called "negative" is the result of an arbitary decision by Benjamin Franklin to call one the rubbed objects in his experiments (a glass rod which happened to have a deficiency of electrons) "positive". A rubber rod rubbed with fur has opposite charge. To understand why would require a complex theoretical anaylsis of the rubbing process and the electron affinity of the two materials being rubbed.
For more about that, see http://books.google.com/books?id=OwdAkGQ3AZYC&pg=PA605&lpg=PA605&dq=%22Benjamin+Franklin%22+positive+glass+rod&source=web&ots=snTL0UzdS0&sig=jwzFMxLfLsGBRqB9855g6W2yzso&hl=en&sa=X&oi=book_result&resnum=1&ct=result
thank you very much for the links.
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