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A plastic rod has a uniform negative charge distribution, as shown in the diagram.
What happens to the charge on the rod when one part of the plastic rod touches a neutral metal sphere set on an insulating stand?
All the negative charge on the rod is transferred into the metal sphere, leaving the plastic rod neutral.
Only the negative charges that touch the metal sphere are transferred onto the sphere. The plastic rod still has some negative charge on it.
The rod gains more excess negative charges by taking them from the metal sphere and increasing its negative charge.
There is no transfer of charge when the plastic rod touches the metal sphere. The plastic rod does not change its value of charge.