Electrostatics and Electrical Charges

Electrostatics

• The earliest known study of electrical phenomena dates back to around 700 B.C. in Greece.
• Greeks observed that small pieces of amber (a resin used for jewelry) attracted light materials like straw and seeds when rubbed with animal fur.
• In the 16th century, English physician and physicist William Gilbert (1544-1603) termed substances that exhibit attraction when rubbed as "electrics."
• The term "electricity" comes from the Greek word "elektron," which means amber.

Interactions of Electrical Charges

• In 1733, Francois Dufay studied the repulsive interactions of electricity through experiments with charged bodies.
• Dufay determined that electric bodies can be classified into two groups :
  • Objects with behavior similar to glass rubbed with silk (currently considered positively charged).
  • Objects with behavior similar to a rubber rod rubbed with fur (currently considered negatively charged).
• Bodies within the same group repel each other, while bodies from different groups attract.
• Dufay proposed the existence of two fluids, vitreous and resinous, in a body, where the body in its neutral state has equal quantities of both.
• Benjamin Franklin(1706-1790) proposed that there is a single electric fluid, where an excess of the fluid results in positive electrification and a deficiency results in negative electrification.

Electric Charges

• Electric charge is a fundamental property inherent in matter.
• It resides in the structure of bodies and determines the electric forces.
• Current understanding confirms that matter comprises atoms, each with a dense nucleus of positively charged protons and neutral neutrons, surrounded by lighter, negatively charged electrons orbiting in paths labeled K, L, M, etc.
• In the basic or normal state of an atom, the number of electrons equals the number of protons in the nucleus, and is equivalent to its atomic number Z.

Positive and Negative Charges

• A body is positively charged if it has ceded electrons (having more protons than electrons).
• A body is negatively charged if it has an excess of electrons.

Law of Charges

• Like charges repel, and unlike charges attract.
• Two positive charges repel each, as do two negative charges.
• Positive charges attract negative charges and vice versa.

Principle of Conservation of Electric Charge

• The total electric charge within an isolated system remains constant.
• Electric charge can be transferred from one body to another, but it cannot be created or destroyed.
• The negative charge of an electron is equal in magnitude to the positive charge of a proton.
• This is called charge quantization.

Electric Current

• In experiments conducted in 1731, Stephen Gray discovered that it was possible to electrify a body by connecting it to another through a thread or filament, thus acquiring electricity through friction.
• Materials are divided into two types: conductors and insulators.

Conductive Materials

• Electrical conductors are characterized by having free electrons in their outer orbits, allowing them to move freely throughout the body, jumping from atom to atom, distributing the charge throughout the body's surface.

Insulating Materials

• Electrical insulators (or dielectrics) strongly bind the electrons, thus the atoms do not allow freedom of movement throughout the body, and charge remains static where it is charged, resisting the flow.
• Conductors include silver, iron, water, carbon.
• Insulators include sulfur, bakelite, dry air, rubber, asbestos, cork, glass, mica, paper.

Semiconductors

• Semiconductors, like germanium and silicon, have properties that allow their electrical characteristics to be controlled through adjustments and concentrations of impurities.
• They form the basis for transistors and integrated circuits in electronics.

Electrostatics Defined

• Electrostatics is the branch of physics studying the interactions between charges at rest.

Charging a Body

• A body can be charged by friction.
• Friction involves rubbing two bodies together, causing the electrons in the outer orbits of one to transfer to the other.
• One body gains excess electrons and becomes negatively charged, while the other gains excess protons and becomes positively charged.
• This process alters the body's equilibrium.