Electrostatic Charging Chapter 15

Objectives  If a charged particle attracts a nearby object, must that object have a net charge?  When rubbed with a cloth, a rubber rod acquires a net negative charge. What sign charge did the cloth acquire?  If a proton is brought near one end of a long metal rod (electrically neutral), what is the sign of charge on the far end of the rod?

Conductors and Insulators  Difference: Their ability to conduct, or transmit electric charge  Conductors: good at transmitting electric charge.  Examples: metals  Insulators: poor electrical conductors  Examples: Glass, rubber, plastic

Conductors  In conductors, the valence (outermost) electrons are loosely bound, so they are easily removed from the atom and moved about the conductor of removed from the conductor all together.  Remember, valence electrons are not permanently bound to an atom.

Insulators  In insulators, the loosest bound electrons are too tightly bound to be easily removed from their atoms.  Thus, charge is not available to move through an insulator, nor is it readily removed from the insulator.

Semiconductors  Fall in between conductors and insulators.  Their ability to conduct charge is between insulators and conductors.

Superconductors  An ordinary conductor has only a small resistance to the flow of electric charge.  An insulator has a greater resistance.  Remarkably, in certain materials at sufficiently low temperatures, electrical resistance disappears!  The materials acquire zero resistance to the flow of charge or becomes a superconductor

Superconductors  Once electric current is established in a superconductor, the electrons flow indefinitely.  With no electrical resistance, current passes through a superconductor without losing energy; no heat loss occurs when charges flow.  Applications of superconductors include long-distance transmission of power without loss, and high speed, magnetically levitated vehicles to replace traditional rail trains.

Electroscope  One of the simplest devices used to detect electric charge

Electrostatic Charging  Charging by Friction  Charging by Conduction  Charging by Induction

Charging By Friction  Insulators are rubbed, typically with cloth or fur, and they become electrically charged by a transfer of charge  The transfer of charge here is due to the frictional contact between the materials.  The amount of charge is dependent on the nature of the materials.

Charging by Friction

Charging by Conduction  Conduction = Contact  Conduction refers to the flow of charge during contact where electrons are transferred

Charging by Conduction

Charging by Induction