Download Electric Charges and Static

Electric Charges and Static
Introduction 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.
Net Charge
• 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.
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 Accelerators
Robert 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
Electric charge is quantized
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 +e
an 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)
Continuum of how easily charges flow in a material
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
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…