1) If you are handed an object that you don\'t know if is a conductor or isolato

Question

1)  If you are handed an object that you don't know if is a conductor or isolator, to determine if an object is positive, negative or neutral, repulsion to a probe charge is the only sure test.  Explain.  What if you know beforehand that it is an isolator(or conductor).

2)  A lightening rod is used to controllably discharge atmospheric charges developed during water vapor evaporation and movement in the atmosphere.  Based on the experiments performed (rubbing materials together, electroscope, van de graaff generator), which of the following will be most efficient to make sure the lighting will go through it and not through anything else in the building: a spherical or sharp-edged lighting-rod tip?  Cite the specific experimental demonstration that led you to this conclusion and explain.  

I only have a hunch that the second question, part of the answer towards the end is a spherical shape because we were introduced to the Van de Graaff generator.  

Explanation / Answer

See the second question has been controversial for a long time. But recent stdies have shown that a spherical shaped rod would be better. Go to wikipedia for further details:    

http://en.wikipedia.org/wiki/Lightning_rod#Should_a_lightning_rod_have_a_point.3F  

And remember, lightning rods DONT ATTRACT LIGHTNING, they just provide a low resistance pathway for electricity.

and i didnt understand the first question. If i already know then why do need to do an experiment.?

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