Question

1) A thin neutral metal rod (suspended from non-conducting silk thread) is brought near a highly positively charged sphere. Assume the sphere and rod never touch (and there is no spark).

a) Describe what if anything, happens to the charges inside the metal rod (and why) using the concepts and definitions we covered in class.

b) Draw a free body diagram (force diagram) for the rod. If the net force is not zero, indicate the direction of the net force on the metal rod. Explain your reasoning and use Coulomb's law to justify your answer.   

  

Answer 1

1) Rod surface ( nearer to sphere) becomes negative due to induction. As surface is a large compared to sphere, the induced charge distributes uniformly throughout the surface.

The second surface (away from sphere) of rod attain equal positive charge. Hence potential difference between rod and sphere is low, not sufficient to produce spark.

2) The surface nearest to sphere becomes negative as negative charges are attracted by charged sphere and the other surface attains equally positive charge as it is neutral conductor.

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