7. How can charging take place when the substances are rubbed?

Charging occurs when two materials are rubbed together, a process known as the triboelectric effect or triboelectric charging. During this process, electrons are transferred between the surfaces of the materials, resulting in one material becoming positively charged and the other negatively charged.

Here's a simplified explanation of how charging takes place when substances are rubbed:

1. Contact: When two materials are brought into contact and then separated, there is a transfer of electrons between them. This transfer occurs due to differences in the electron affinity of the materials involved.

2. Electron Transfer: Each material has a different affinity for electrons. One material may have a higher affinity for electrons (electron acceptor), while the other material may have a lower affinity (electron donor). When the materials are rubbed together, electrons are transferred from the material with a lower affinity to the material with a higher affinity.

3. Separation: As the materials are rubbed together, the transferred electrons accumulate on the surfaces of the materials. When the materials are separated, one material carries a net positive charge (due to losing electrons) and the other material carries a net negative charge (due to gaining electrons).

4. Charge Accumulation: The accumulation of positive and negative charges on the surfaces of the materials results in them becoming electrically charged. This charge separation is what leads to the phenomena such as static electricity and attraction or repulsion between the charged objects.

The specific charges acquired by the materials depend on their relative electron affinities and properties. Materials with higher electron affinity tend to acquire a negative charge when rubbed with materials of lower electron affinity, and vice versa. The magnitude of the charge acquired depends on factors such as the surface area of contact, the nature of the materials, and the force of the rubbing action.

Overall, charging occurs during rubbing due to the transfer of electrons between the surfaces of materials, resulting in the accumulation of positive and negative charges and the generation of static electricity.