16 – 1 Electric charge

Structure of the Atom small, dense nucleus Contains protons and neutrons surrounded by electron cloud Protons are + charged Electrons are – charged Neutrons are neutral (no charge)

Properties of electric charge: There are 2 kinds of charge; ( + ) and ( - ) Similar charges repel and opposite charges attract

Properties of electric charge con’t: Charge is conserved Charge can be transferred from one object to another but not created or destroyed

Properties of electric charge con’t: Charge is quantized. It comes in discreet amounts Fundamental unit of charge = e This is the charge on a proton or electron, e = 1.60x10 -19 C SI unit of charge is the coulomb,C

Millikan Oil-Drop Experiment Measured the elementary charge, e Found every charge had an integral multiple of e qt = n e

Atomic Particles Particles Charge ( C) Mass (kg) Electrons Protons -1.60x10-19 9.109 x 10-31 Protons +1.60x10-19 l.673x10-27 Neutrons

Objects can be classified into categories based on how they transfer charge. Conductor Insulator Semiconductor Superconductor

Conductor Transfers charge easily, outer electrons are loosely bound to atoms Ex: metals like gold, silver, copper

Insulator Materials that do not transfer charge easily, outer e- bound tightly to atom Example: rubber, glass

Semiconductor – insulator in pure state, good conductor when small impurity is added Ex: Silicon, Germanium

Superconductor – material becomes a perfect conductor (no resistance) at or below a certain temperature Ex: Zinc, Aluminum, Tin & Mercury

Most materials can be charged by friction but only conductors can be charged by induction

Polarization In most neutral atoms or molecules, the center of positive charge coincides with the center of negative charge. in presence charged objects, the centers my shift slightly

Examples