Topic 6. Charge Interactions

Topic 6. Charge Interactions

1. History of Electricity: from Greeks to Superconductivity

   • Around the year 624 BC
     • Thales of Miletus discovered that a yellow petrified tree resin called elektron
       • From the Greek discovery there have been multiple experiments to understand the electric phenomena.

2. Concept of Electric Charge and its Interactions

   • The charges of the atom are negative and positive.
     • If there is the same number of positive and negative particles the atom is neutrally charged.
     • If there is an excess of positive or negative particles the atom (ion) will have a positive or negative electric charge.
     • The number of electrons in the outermost energy level of atoms of a material is determined identifying if it is a charge conductor or not.
       • The charges interact with each other when they are close. Equal charges repel each other
       • Different charges will attract each other

3. Coulomb’s Law and Continuous Distributions

   • In 1780 Charles Coulomb performed many experiments to find it. He designed a torsion balance experiment, in which the electric force causes torsion in a thread that is suspended from its upper end
     • The angle formed by the torsion of the thread is used to calculate the magnitude of the electric forces.
       • “The electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the distance between the two objects”
         • Coulomb’s law is useful to calculate the force acting in a pair of point charges.