A physics teacher demonstrates electrostatic effects to their class. They rub a glass rod with a dry silk cloth so that the rod gains a net positive charge. The teacher then holds the charged glass rod close to a thin, steady stream of ethanol running from a burette, and the stream bends towards the rod.
Explain, in terms of moving charges, how the glass rod becomes positively charged.
Explain why the stream of ethanol bends towards the positively charged rod.
Suggest why the charge remains on the glass rod even when it is being held by one end.
Suggest why this demonstration does not work so well when the air is humid.