Question

A conducting sphere with radius 4.0cm has a net positive charge on it. The sphere is then connected with a metal wire to a second, uncharged, sphere of radius 1.0cm.
Which statement below BEST describes the flow of electrons when the metal wire connects the two spheres?
A) Electrons flow from the 4.0cm radius sphere to the 1.0cm radius sphere leaving the 4.0cm radius sphere with a net charge of zero.
B) Electrons flow from the radius 1.0cm sphere to the 4.0cm radius sphere, until both spheres have net positive charge.
C) Electrons flow from the 4.0cm radius sphere to the 1.0cm radius sphere, until both spheres have net positive charge.
D) Electrons flow from the radius 1.0cm sphere to the 4.0cm radius sphere, until the surfaces of both spheres are at the same potential.
E) Electrons do not flow along the wire, because the system is already in equilibrium.

Answer 1

Hint: Here two spheres are given, one with a net positive charge and another sphere has a net charge zero in it. When these spheres are connected with a metal wire, electrons start flowing from one neutral body to the other, until the net charges are equal.

Complete answer:
Charging by conduction involves connecting a charged object to a neutral object. Upon contact, charges will flow from the charged object to the other object. If a sphere with a net negative charge is connected to a neutral body, electrons will flow from the charged sphere to the other, until their net charge is negative. Now consider a sphere with a net positive charge connected to a neutral body. The positively charged body has an excess of protons in it, and protons are tightly bound by the nucleus. Therefore, it cannot leave the charged body. But, these protons are capable of attracting the electrons from the neutral body. Hence, electrons will flow from the neutral body to the positively charged body, until their net charges are equal.
Here, the 4.0cm sphere has a net positive charge and the 1.0cm sphere is neutral. Hence, Electrons flow from the 1.0cm radius sphere to the 4.0cm radius sphere until both spheres have net positive charge.

Answer is option B.

Note:
The law of conservation of charge is observed during the charging by conduction process. It states that charge is always conserved. When all objects involved are considered prior to and after a given process, we can see that the total amount of charge among the objects before the process is the same as after the process.