Electric Charges and StaticIntroduction to Electricity

Let review…

• All matter is made up of atoms.• Atoms are made of charged subatomic

particles.

• Electric charge is a fundamental property of matter, similar to mass.• The electromagnetic force exists between protons and electrons. Like charges repel. Opposite charges attract.• Unlike mass, charges can positive or negative.

• An object is electrically neutral when it has equal amounts of positive and negative charges.

• Most matter is neutral.• Objects can gain or lose charge, usually by coming

into contact and rubbing against each other. • If the object picks up electrons, it will have an

excess of __________ charges and therefore will be ____________ charged.

Net Charge

Static Electricity

• It only requires a tiny imbalance of charges to create static electricity.

Examples of how objects become charged:• Socks tumbling in a dryer can pick up charge• Socks crossing on a carpeted surface on a dry day• Sliding into or out of a car seat on a winter (dry) day.• Rubbing a balloon on your hair• Rubbing a wool cloth on a nylon bar

When the charges come back together quickly, you can feel it and sometimes see it!

Nature’s Static Electricity

http://www.fas.org/irp/imint/docs/rst/Sect14/Sect14_1d.html

Van de Graff generator

Particle AcceleratorsRobert Van de Graff was using high voltage (potential charge difference) to move charges. Scientists became very interested in moving charges quickly enough to “crack into” the nucleus of atoms.Linear accelerators allowed scientists to move charges faster, and with less voltage, than Van de Graff generators. The limits of linear accelerators inspired scientists to create circular accelerators called cyclotrons. The circular method would thus allow an electric field alternating at a constant frequency to kick particles to ever higher energies. (http://www.aip.org/history/lawrence/epa.htm)

For your viewing pleasure: http://www.phdcomics.com/comics/archive.php?comicid=1489

In 1909, Robert Millikan performed the well-known “oil drop” experiment over and over again until he determined the following:

when an object is charged, its charge is always a fundamental unit of charge (e)

In other words, charges occur in discrete amounts e, 2e, 3e…

As more work in the field was done, scientists defined:a proton has a charge of +ean electron has a charge of –e

After yet more work, the value of e was determined:e = 1.6 x 10-19 C (coulomb is the SI unit for charge)

Electric charge is quantized

Superconductor Conductor Semiconductor Insulator

• Semiconductors in their pure state rank as indicated above, BUT by “doping” semiconductors, their ability to conduct electric charge can be increased significantly– Examples: Silicon or Germanium are well used, Carbon, Boron and

Aluminum can also be altered

• Superconductors are certain metals that become perfect conductors are extremely low temperatures. Scientists are looking for a superconducting material that works at less extremely cold temps.

- Examples: http://youtu.be/8fgjIwnsU7Y- 10 min TedTalks video about superconducting: Superconducting

Continuum of how easily charges flow in a materialEasily Not Easily

Transferring Electric Charge• Charged by contact

• Applies to insulators and conductors

• Charged by induction• Applies to conductors

Transferring electric charge cont’d…

• Charged by polarization• Applies to insulators

When an object becomes polarized, it has no net charge but is still able to attract or repel objects due to this realignment of charges.

Example: a balloon ‘sticking’ to a wall a comb ‘bending’ water combing paper dots

More to come…• Separating charges and moving charges create

and manipulate FORCES!

• This big topic will be for a new day…