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