Understanding Electricity: Charges, Conductors, and Coulomb’s Law
The word electricity comes from the Greek word “elektron.” There are two types of electric charges: positive and negative. The origin of electric charge is the atom.
Electric Charge and Atomic Structure
The proton has a positive electric charge, the neutron has no electric charge, and both are located in the nucleus. The electron has a negative electric charge and orbits the nucleus. A neutral atom has an equal number of electrons and protons. If an object’s atoms lose electrons, it will have an excess of protons and a positive charge. If an object’s atoms gain electrons, it will have an excess of electrons and a negative charge.
Electrical charge is denoted by “q” and is measured in coulombs (“C”). The electron’s charge is -1.6 x 10-19 C, and its mass is 9.11 x 10-31 kg. The proton’s charge is +1.6 x 10-19 C, and its mass is 1.67 x 10-27 kg. The neutron has no charge and a mass of 1.67 x 10-27 kg.
Properties of Electric Charge
- Conservation of Charge: If two initially neutral objects are rubbed together, charge is not created. Instead, electrons are transferred from one object to the other.
- Quantization of Charge: When an object is electrically charged, its charge is always a multiple of the fundamental unit of charge, denoted by “e,” which is approximately 1.6 x 10-19 C.
- Charge Interactions: Like charges repel, and unlike charges attract.
Power Classification of Materials
Materials are classified as conductors, insulators (or dielectrics), and semiconductors.
- Conductors: These materials have electrons that are weakly bound to their atoms, allowing them to move freely within the material. These electrons are called free or conduction electrons (e.g., metals).
- Insulators (or Dielectrics): In these materials, electrons are tightly bound to their atoms, making it difficult for electric charge to move (e.g., glass, wood).
- Semiconductors: These materials have conductivity that varies with temperature.
Ways to Electrify a Body
A body can be electrified in several ways:
- Friction: When two bodies are rubbed together, enough energy is transferred for their atoms to interact. One body gives up electrons, and the other captures them, resulting in different charges on each body.
- Contact: When an electrified body (either negatively or positively charged) touches a neutral body, there is a transfer of electrons. If a negatively charged body contacts a neutral one, the latter captures electrons from the first, becoming negatively electrified.
- Electrostatic Induction: Consider a neutral conductor. If a positively charged body is brought near the conductor, the conductor’s free electrons are attracted to the positively charged body and accumulate on that side (let’s call it side A). Side B will then have an excess of positive charges. This separation of charges in the conductor, caused by the approach of an electrical body, is called electrical induction. Note that the body as a whole remains neutral.
* Blown want desir excess charges.
Coulomb’s Law
1 Coulomb (C) is approximately equal to 6.25 x 1018 electrons. The charge of a body, “q,” can be measured by the number of electrons the body loses or gains (n * e). However, this form of expressing the value of the load is not practical. In practice, the coulomb is used. When we say a body has a 1C load, it means it has gained or lost 6.25 x 1018 electrons.
The force that attracts or repels two charges is directly proportional to the product of the charges (q1 x q2) and inversely proportional to the square of the distance (r) between them.
The proportionality constant (K) is measured in 9 x 109 Nm2/C2. “r” is the distance between the charges in meters (m). Examples: If the distance is doubled, the force is decreased by a factor of 4. If the distance is reduced by a factor of 3, the force increases by a factor of 9. F < 0 = force of attraction, F > 0 = force of repulsion.