Transcript Static Electricity Ideas

Static Electricity
Define some of the major ideas about
static electricity
Static Electricity
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Electricity “exists” because of two types of charge
Charge is (+) or (-)
Fundamental unit is the charge of one electron = one proton =
1.6 x 10-19C
Unit of charge is the Coulomb. One coulomb is a boatload of
electrons
Like charges repel, opposites attract
Charge is Quantized, you can’t have ½ of an electron charge.
Can’t break the charge on one electron any smaller.
Static Electricity
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Ways to charge objects include:
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Friction, like rubbing the fur on plastic
Conduction, touching a charged object to another
object
Induction, like in the lab (which maybe didn’t work
too well). Bring a charged object next to a
conductor and then “ground” the conductor,
leaving it charged.
Static Electricity
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Insulators: electrons are held tightly and can’t
move around easily, so electricity doesn’t
move through them. Examples are rubber,
plastic, glass
Conductors: charge (electrons) moves easily.
Examples are metals: copper, aluminum, gold
Static Electricity
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Electric Force
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You saw the tape attract or repel, what causes things to
move? (rhymes with horse)
There is an electric force between any 2 charged objects
called the Coulomb Force
Force depends on the amount of charge on each object
and on the distance between them. This force is analogous
to the Universal Gravitational Force. Can you write the
equation for these?
Electric Force
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Coulomb’s law for electric force
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F = (kq1q2)/r2
q = amount of charge in coulombs
r = distance between charged objects
k = Coulomb constant = 9x109
The force is the same on both charged objects
(remember forces exist in pairs, Newton’s 3rd law)
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Electric Force
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The electric force is conceptually much
bigger than the gravitational force.
Why don’t we see the “electric force” much?
Objects in our world are typically neutral
(even number of electrons and protons)
Electric Field
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Much like the concept of an invisible Gravitational
Field, there exists an invisible electric field around
any charged object.
The Electric field is defined as the Force that
another charged object (test charge) would feel in
the presence of the source charged object divided
by the amount of the charge on the test charge
E = F/q = kQq/r2q = kQ/r2
Electric Field Lines
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Electric field lines surround a charged object
and point in the direction that a positive (+)
test charge would be forced to move