Download Static Electricity

Electrostatics
the study of electrical
charges at rest
Electrodynamics
the study of electrical
charges in motion
Two opposite types of charge exist, named
positive and negative by Benjamin Franklin.
Charge is a
property of
matter.
Charged particles exist in atoms.
Electrons are responsible
for negative charge;
protons for positive charge;
neutrons have no charge.
Small amounts of ordinary matter contain
incredible amounts of subatomic particles!
Choose an element on the periodic table.
Iron has atomic number of 26. This means that
there are 26 protons in each atom of iron.
Assuming that the iron atom is neutral (no net
charge), the atom will also have 26 electrons.
The number below the element is the atomic mass. This number tells us
that on average, each atom of iron has a total of 55.845 protons and
neutrons in the nucleus. Since there are exactly 26 protons in an atom
of iron, on average each iron atom has 29.845 neutrons.
How is that possible? The number of neutrons in the iron atom can
vary. Some isotopes of iron contain exactly 29 neutrons, some have 28,
and some have 30.
Different isotopes of iron may be expressed as Fe-55, Fe-56, Fe-57, etc...
The atomic mass also tells us the mass in grams of one mole of iron.
Charged atoms are known as ions.
An atom becomes charged by gaining or losing
electrons.
The charge of an ion is typically expressed as an
exponent written after the atomic symbol.
Cu+2 represents a copper atom with a +2 charge,
which means that it is a copper atom that lost 2
electrons.
Cu-1 represents a copper atom with a -1 charge,
which means that it is a copper atom that gained
an electron.
Let’s count the number of subatomic
particles (protons, neutrons, and electrons)
in a relatively small amount of an element.
Let’s assume that a penny is pure copper and has a mass
of 3.4 grams. Checking the periodic table, we find that the
atomic number of copper is 29 and its atomic mass is 63.546.
This means that 6.022 x 1023 atoms of copper (= 1 mole =
Avogadro’s number) has a mass of 63.546 grams, and each
individual atom contains 29 protons, 29 electrons, and on
average, 34.546 neutrons.
Therefore, the number of copper atoms in a 3.4 gram penny is
found by multiplying Avogadro’s number by 3.4/63.546. This
value is then multiplied by 29 and 34.546 to determine the
approximate numbers of subatomic particles in the penny.
How long would it take to count them????????
Conductor
material that allows charges to move about easily
Insulator
material through which charges will not easily move
Basic Law of Electrostatics:
Like charges repel; unlike charges attract
Click here to read about charging objects
by contact (friction). See shoes on carpet
here. See a balloon on your sweater here.
View a simulation
of charging a
balloon by rubbing
it on your hair
and then sticking
it to a neutral
wall here.
The SI unit of charge
is the Coulomb,
named in honor of
Charles Augustin Coulomb.
1 C = charge on 6.25 x 1018 electrons (or protons)
1 e- = 1.60 x 10-19 Coul = elementary charge
How many Coulombs of negative charge are
contained in that copper penny?
COULOMB’S LAW
The force between two charged objects is
directly proportional to the product of their
charges and inversely proportional to their
separation distance squared.
link1, link2, link3, link4, link4
In equation form:
q
q
F = k 12 2
d
F is the force of attraction, measured in NEWTONS,
between charges q1 and q2
k is the Universal Electrostatic Constant, equal to
9.00 x 109 N m2/coul2
q1 and q2 are the attracting charges, measured in
Coulombs
d is the distance between the charges,
and is measured in METERS
Electric Fields
An electric field exists in a region
if space if a charge placed in that
region experiences an electric force.
The magnitude of an electric field at any
given point is defined to be the ratio of
the force on a
charge at that
point to the
amount of charge.
E = F/Q
Electric field strength has units
of Newtons/Coulomb (N/C).
The direction of the electric field at any point is defined
to be the same direction as the direction of force on a
positive test charge placed in the region at that point.
Field lines point
away from positive
charges and toward
negative charges.
Investigate electric fields
due to point charges
at the simulation here.
Click here to view a
simulation showing the
magnitude and direction
of the electric force on a
test charge when placed
near other charges.
Click here to view a
simulation of a charged
particle moving through
a region occupied by
other charges.
Electric Potential Difference
the change in
electric potential energy
per unit charge
V = W/Q
The SI unit of electric potential
difference is the VOLT, named in
honor of Alessandro Volta.
One VOLT is the electric potential
difference between two points when one Joule
of work is done in moving one Coulomb
of charge between the points.