A small neutral conducting sphere is mounted on an insulating stand
PHYSICS · Multi-part · CBSE · Physics · Electric Charges and Fields · Electric Charges and Fields
Problem
A small neutral conducting sphere is mounted on an insulating stand. A student slowly brings a negatively charged plastic rod close to (but not touching) the left side of the sphere and then, while the rod remains in place, connects the right side of the sphere to ground with a thin wire. After a few seconds, the student first removes the grounding wire and only then withdraws the charged rod to a distant location.
Assume no other charges are in the vicinity and ignore any mechanical or thermal effects.
(a) Describe qualitatively how the free electrons in the sphere move immediately after the negatively charged rod is brought near but before the sphere is grounded. Indicate which side of the sphere becomes relatively positive and which becomes relatively negative during this stage.
(b) While the rod is still present and the grounding wire is connected, explain the direction of charge flow between the sphere and Earth. State the sign of the charge that leaves or enters the sphere.
(c) After the grounding wire has been removed but the rod remains, the sphere is isolated. Use the law of conservation of electric charge to predict the net charge on the sphere at this instant. Justify your answer.
(d) Finally, the rod is withdrawn to a distant location. Describe the final distribution of charge on the sphere and determine its net charge. Explain how each step in the sequence leads to this result.