A positively charged rod is brought near two uncharged...

A positively charged rod is brought near two uncharged conducting spheres of the same size that are initially touching each other (diagram a). The spheres are moved apart, and then the charged rod is removed (diagram b). (a) What is the sign of the net charge on sphere 1 in diagram b? (b) In comparison with the charge on sphere 1, how much and what sign of charge is on sphere $2 ?$

Key Concepts

Electrostatic Induction

Electrostatic induction is the process by which a charged object causes a redistribution of charges within a nearby neutral conductor without direct contact. The presence of the external electric field makes free electrons in the conductor move, leading to regions of positive and negative charge within the conductor, even though the total charge remains zero.

Charge Redistribution in Conductors

In conductors, charges are free to move throughout the material. When an external charge is brought near, the free electrons migrate under the influence of the electric field. This movement results in a separation of charge within the conductor, with one side accumulating excess electrons (negative charge) and the other becoming electron-deficient (positive charge).

Separation of Charges Upon Isolation

When parts of a conductor are isolated or separated after induction, the charge separation can be maintained as the conductive pathway that allowed electrons to redistribute is no longer present. This isolation 'locks in' the separated charges, resulting in permanent regions of net negative and positive charge on the separate objects.

Conservation of Charge

The principle of conservation of charge states that the total electric charge in an isolated system remains constant. Although the distribution of charge can change due to processes like induction, the total net charge does not change. This is why a system that begins electrically neutral will, after being subjected to induction and subsequent separation, have objects with equal and opposite charges.

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