When a negatively charged plastic rod touches a neutral sphere, the process that occurs is called charging by conduction. Here's how the negative charges will spread throughout the sphere:
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Contact: When the negatively charged rod comes into contact with the sphere, the excess negative charges (electrons) on the rod can move to the sphere since the sphere is conductive.
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Distribution: As the electrons move to the sphere, they will redistribute themselves across the surface of the sphere. This is because like charges (negative charges in this case) repel each other, causing the electrons to spread out as much as possible to minimize their mutual repulsion.
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Equilibrium: Eventually, a stable distribution of negative charge will be achieved on the surface of the sphere. Due to the symmetrical shape of the sphere, the negative charge will tend to spread evenly over the surface.
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Separation: Once the rod is removed from the sphere, the sphere will retain the excess negative charge that has transferred to it, meaning it will now be negatively charged.
In summary, when the negatively charged rod touches the sphere, electrons move from the rod to the sphere and spread evenly over the surface of the sphere due to repulsion among the like charges, resulting in the sphere becoming negatively charged.