Lecture 1 - Charge and Charging Processes

Lecture 1 - Charge and Charging Processes

1. Two types of forces

   • Like charges repel each other
     • REPULSIVE
   • Opposite charges attract each other
     • ATTRACTIVE

2. CONSERVATION OF CHARGE

   • Charge is not created or destroyed
   • Adding electrons to one object means taking them from another source
     • The object may be the Earth

3. ATOMS

   • No Net Charge
   • Number of Protons = Number of Electrons
   • Q = 0C
     • Charge measured in Coulombs

4. Charged Atoms (IONS)

   • Adding electrons
     • More negative electrons than positive protons
     • Net negative Charge
       • -Q
   • Removing Electrons
     • More positive protons than negative electrons
     • Net positive Charge
       • +Q
   • Q = += Ne
     • -Q
       • N = number of excess electrons
     • +Q
       • N = number of missing electrons
     • Q is treated as a continuous variable

5. Static Electricity

   • Explained by the transfer of electrons
     • Rubbing enhances the contact area and makes the transfer of electrons easier
   • Electrons are removed from some objects
     • They become positively charged
   • Electrons are added to some objects
     • They become negatively charged
   • Net transfer is 0C

6. Why are uncharged insulators attracted to charged objects?

   • Charged object causes the electron clouds of the atoms in the insulator to become slightly distorted
     • Positively Charged Object
       • Electron cloud moves towards the positive charge
         • Other end becomes more positive than usual
     • Negatively Charged Object
       • Electron Cloud moves away from the positive charge
         • Other end becomes more negative than usual
     • Insulator is said to be POLARISED
       • Causing the insulator to move towards the charged object

7. Electrostatic Induction

   • Mobile Conduction Electrons
     • Allow a charged rod to attract small pieces of uncharged metal foil
   • CONDUCTION OR FREE ELECTRONS
     • The electrons that detach from their parent atom
       • Net Positive Charge
   • Charging Conductors
     • Electrons are transferred to or from an object when in contact with another
       • Charge is conserved
     • Charge by Contact and Electrostatic Sensitive Devices (ESD)