Question

Consider a neutral conducting sphere. A positive point charge is placed outside the sphere. The net charge on the sphere is then:
A) Negative and distribute uniformly over the surface of the sphere
B) Negative and appears only at the sphere closest to the point charge
C) Negative and distribute non-uniformly over the entire surface of the sphere
D) Zero

Answer 1

Hint: Since the point charge is placed outside the sphere and there is no physical contact between the sphere and the charge, we should consider the process of charging by induction. Induction charging is a method used to charge an object without actually touching the object to any other charged object. An understanding of charging by induction requires an understanding of the nature of a conductor and an understanding of the polarization process.

Complete step by step solution:
When the positive point charge is brought near the sphere, the presence of a positive charge induces a mass migration of electrons in the sphere from the side away from the charge to the side facing the charge. Due to the accumulation of electrons, the side of the sphere facing the charge develops a negative charge and the side facing away develops a positive charge. Since no external charge has been given to the sphere and there has just been a redistribution of charges due to induction, we have to keep in mind that the sphere is electrically neutral. Due to this, equal charge separation takes place and the positive charge will equal the negative charge.

Hence net charge is zero and therefore, option (D) is the correct answer.

Note: If there was a two-sphere system in contact placed near a positive charge in the same manner as stated in the question, then they will be polarized due to induction and the sphere nearer to the charge will develop a negative charge and the sphere away from the charge will develop a negative charge. When the two spheres are separated, one will be negatively charged and the other will be a positive charge. In this case, the net charges on the sphere will not be zero.