22.3:
Conductors and Insulators
Atoms consist of a positively charged nucleus surrounded by electrons, which form a cloud. Attractive electrical forces bind the nucleus and the electrons together.
In some materials, electrons are loosely bound to the nucleus. For example, a copper atom consists of 29 protons and 29 electrons. However, one electron is loosely bound to the nucleus and is free to move.
The total number of free electrons equals the total number of atoms in the wire, which can move around the entire wire. Thus, when an external source of charge comes into contact with copper, electrons quickly move through the wire. Most metals, like iron, gold, and silver, conduct electricity, and are called conductors.
However, materials like wood, glass, paper, and silk do not have free electrons. Their atomic structure is such that all the electrons are firmly bound to the nucleus. Thus, they are insulated from conducting charges and are called insulators.
Hence, whenever they are charged by rubbing against each other, the excess charges remain on them, leading to electrical forces.
22.3:
Conductors and Insulators
Some materials may easily let electrical charges pass through them, while others obstruct their flow. The former are called conductors and the latter insulators. The atomic structures of materials determine whether they are conductors or insulators of electricity.
Most metals are conductors. Their atomic configuration is such that one or more electron(s) are loosely bound to the nucleus in each atom. Thus, a sea of mobile electrons are available in them, known as free electrons. Their easy movement neutralizes any external charge added to the conductor. Hence, metals cannot harbor excess charge and do not experience electrical forces mutually or with other materials.
Human bodies are good conductors of electricity. For example, excess charges accumulate when someone rubs their shoes against a carpet fiber or an insulator. If they then touch a charged conducting material like a doorknob, they receive an electrical shock because of the rapid flow of charges.
Unlike conductors, insulators have atomic structures that do not allow any electrons to move between atoms freely. Thus, any excess charge added to insulators remains in the material. These excess charges can then lead to electrical forces between insulators. Plastic, wood, glass, and fur are typical examples of insulators.
Suggested Reading
- OpenStax. (2019). University Physics Vol. 2. [Web version]. Retrieved from https://openstax.org/details/books/university-physics-volume-2; section 5.2; page 188.
- Young, H.D and Freedman, R.A. (2012). University Physics with Modern Physics. San Francisco, CA: Pearson; section 21.2; page 691.