A student rubs a polythene rod with a dry woolen cloth so that the rod gains a negative charge. She then holds the charged rod close to a thin, steady stream of tap water, and the stream bends towards the rod.
Explain, in terms of moving charges, how the polythene rod becomes negatively charged.
Explain why the stream of water bends towards the negatively charged rod.
Suggest why the charge remains on the polythene rod even when it is being held by one end.
Suggest why this demonstration does not work so well when the air is humid (damp).