Question

When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.

Answer 1

Hint: This phenomenon is observed while rubbing two non-conductive surfaces. In a non-conductive surface the charge is stored at a particular location of the material. When we rub two objects a charge transfer occurs. Some of the electrons go from one material to the other. We know gain of electron gives -ve charge and loss of electron gives +ve charge.

Complete step by step answer:
Static electricity is an imbalance of electrical charge on the surface of a material. The charge will stay on the material unless it can find a path. We can create the condition of static electricity if we rub one material with another.

When we rub two non-conducting materials together, electrons from one object are transferred to the other object. The relative charge of the materials depends on the force by which the electrons are bound to the material. Generally, the object with relatively weaker force of attraction loses its electron to the other material. When a molecule or atom loses its electron, it gains a relative positive charge. Whereas, when the atom/molecule gains electrons, it gains a relative negative charge.

In this example, the electrons move from the glass to the silk. As a result, the silk gains a relative negative charge, and the glass rod attains a positive charge.

So, we can say for sure that the law of conservation of charge is still true in this case. No charge is created in this phenomenon. Charge is only transferred from one object to the other.

Note: The law of conservation of charge states that the total electric charge in an isolated system never changes. That is why both the materials have the same charge, but they are of opposite polarity. Net charge of the system is still zero.