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How can you charge a metal sphere positively without touching it?

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Figure (a) shows an uncharged metallic sphere on an insulating metal stand.
Bring a negatively charged rod close to the metallic sphere, as shown in Fig. (b).
As the rod is brought close to the sphere, the free electrons in the sphere move away due to repulsion and start piling up at the farther end.
The near end becomes positively charged due to deficit of electrons.
This process of charge distribution stops when the net force on the free electrons inside the metal is zero.
Connect the sphere to the ground by a conducting wire.
The electrons will flow to the ground while the positive charges at the near end will remain held there due to the attractive force of the negative charges on the rod, as shown in Fig.(c).
Disconnect the sphere from the ground. The positive charge continues to be held at the near end [Fig. (d)].
Remove the electrified rod. The positive charge will spread uniformly over the sphere as shown in Fig. (e).
In this experiment, the metal sphere gets charged by the process of induction and the rod does not lose any of its charge.
Similar steps are involved in charging a metal sphere negatively by induction, by bringing a positively charged rod near it. In this case the electrons will flow from the ground to the sphere when the sphere is connected to the ground with a wire.
answered May 28, 2014 by meena.p

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