Tourigny­Conroy
Electrostatics
Recall: All matter is made up of atoms which
are, in turn, made up of protons (+), neutrons
and electrons (­).
Atoms will combine in specific ways to create
molecules and, in turn, macroscopic objects. These
objects contain millions of positive and negative
charges.
Classifying Matter
The ability of atoms (or molecules) to 'hold onto' electrons determines the
classification of materials into three categories:
1. Conductors ­ electrons are free to move within the material
2. Insulators ­ electrons are fixed in place
3. Semi­Conductors ­ electrons are fixed in place, however, with enough
voltage they can break free
Representing Charge
For simplicity, we use '+' and '­' signs to represent many protons and electrons.
This allows us to represent things like:
net charge
charge distribution
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Tourigny­Conroy
Electrostatics
Charge Quantization
Charge is said to be quantized. This means that there exists a smallest amount
of charge, the elementary charge, e
Where, e = 1.6 x 10­19C
(C is Coulombs)
Therefore, the charge of a single ...
­ proton = +e = +1.6 x 10­19C
­ electron = ­e = ­1.6 x 10­19C
Net Charge
The net charge, Q, of an object refers to the excess number of electrons or
protons.
Ex. How many excess electrons are in a net charge of ­5.0 C?
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Tourigny­Conroy
Electrostatics
Principles of Electric Charges
The fundamental principles of electrostatic charges are:
The Law of Electric Charges
­ Opposite charges attract each other
­ Like charges repel each other
­ Charged objects attract some neutral objects
Law of Conservation of Charge
The net charge within an isolated system is conserved.
Coulomb's Law
We know that two charged particles experience a mutual force of attraction
or repulsion.
In a series of experiments, Charles Augustin de Coulomb experimentally
established that..
This leads us to Coulomb's Law:
Ex. Calculate the force of repulsion between two +2.0 C charges that are
separated by a distance of 50 cm.
Ex. The force of attraction between two charges is found to be 0.01 N.
Calculate the force of attraction if the distance between them is halved and
the magnitude of one of the charges is doubled.
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