Electric Charge and Electric Force

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• Electric Charge and Electric Force

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• Matter is made up of atoms.
• Atoms are made up of
• Electrons
• Protons
• Neutrons

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• ATOM
• Electrons are negatively charged
• Protons are positively charged
• Neutrons have no charge

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• A non moving accumulation of net charge is called
  static charge.
• Electrostatics is the study of electrical charges
  that can be collected and held in place.

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• OBJECTS CAN BE
• Conductors
• Insulators
• Semi-Conductors
• Super Conductors

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CONDUCTORS

• Conductors are materials that electric charge can
  move through easily. Their outer (valence)
  electrons are loose.
• Ex copper, silver earth

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An object connected to the Earth, or the ground,
by a good conductor, is said to be grounded.
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INSULATORS

• Insulators are objects that dont allow electrons
  to move through them easily. Their valence
  electrons are tightly held.
• Ex plastic, wood,
• rubber glass

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SEMICONDUCTORS

• Semiconductors are materials that behave as
  insulators or conductors. Their valence
  electrons are tightly held until given a small
  energy boost.
• Ex silicon, germanium

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SUPERCONDUCTORS
Some materials become superconductors below their
critical temperature (near 0 Kelvin absolute
zero). They have zero resistance to charge
movement.
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ELECTRIC CHARGE

• IS AN ELECTRICAL PROPERTY THAT CREATES A FORCE
  BETWEEN OBJECTS.
• POSITIVE
• NEGATIVE
• NO CHARGE (NEUTRAL)

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AN OBJECT IS

• POSITIVE when it has more protons
• NEGATIVE when it has more electrons
• NEUTRAL when it has same number of protons and
  electrons (no charge)

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ELECTRIC CHARGE

• Is measured in Coulombs (C)
• Electron Charge-1.6 x 10-19C
• Proton Charge1.6 x 10-19C

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ELECTRIC CHARGE

• 1.0 coulomb of charge equals 6.25 x 1018 protons
• -1.0 coulomb of charge equals 6.25 x 1018
  electrons

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CHARACTERISTICS OF ELECTRIC CHARGE

• 1. There are three kinds of charges - positive,
  negative, and neutral
• 2. Like charges repel each other and unlike
  charges attract each other.

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Like charges repel
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Unlike charges attract
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CHARACTERISTICS OF ELECTRIC CHARGE

• 3. Charges have a natural tendency to be
  transferred between unlike materials.
• 4. Electrical charges are always conserved.

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CHARACTERISTICS OF ELECTRIC CHARGE

• Charges are quantized. If an object is charged,
  its charge is always a multiple of a fundamental
  unit charge
• 1.6 x 10-19 C.

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CHARACTERISTICS OF ELECTRIC CHARGE

• 6. The SI unit of charge is Coulomb (C).
• 7. Objects can be charged by friction, contact,
  polarization and induction.

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CHARGING OBJECTS
Protons and neutrons are relatively fixed in the
nucleus, but the outermost electrons in some
atoms can be easily transferred from one atom to
another
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CHARGING OBJECTS
Objects gaining electrons are negatively
charged Objects losing electrons are positively
charged
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EARTH
Is an infinite reservoir of electrons. It can
accept and supply an unlimited number of
electrons.
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When a conductor is connected to Earth by means
of a conducting wire or copper pipe, it is said
to be grounded.
Ex plumbing fixtures, metal faucets, sinks
pipes.
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CHARGING METHODS

• Friction
• Contact
• Induction
• Polarization

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FRICTION

• Electrons can transfer from one material to
  another when they are rubbed against each other.

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Rubbing glass rod with silk
Silk will gain electrons and glass rod will lose
electrons. Glass?positively charged Silk?negativel
y charged
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Rubbing rubber with fur
Rubber will gain electrons and fur will lose
electrons. Fur?positively charged Rubber?negativel
y charged
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CONTACT

• Electrons can transfer from one material to
  another when the two materials touch.

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INDUCTION
Is the process of charging an object by grounding
it while it is near another charged object. When
an object is charged by induction, its charge is
opposite to that of the charging object.
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INDUCTION
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Induction
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POLARIZATION
In insulators, the presence of a charged object,
results in more positive charge on one side of
the molecule than the other.
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POLARIZATION
Insulator
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POLARIZATION
The rearrangement of charges within individual
molecules produces an induced charge on the
surface of the insulators. This effect is known
as polarization.
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ELECTROSCOPE
Is a device used to detect the presence of
electrical charges.
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ELECTROSCOPE
http//www.shep.net/resources/curricular/physics/P
30/Unit2/electroscope.html
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LIGHTNING
A lightning bolt occurs when billions of
electrons are transferred at the same time.
Lightning bolts also occur between the negative
area of one cloud and a positive area
of another cloud.
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LIGHTNING
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LIGHTNING
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LIGHTNING
Lightning is a large discharge of static
electricity. The friction from the movement of
water droplets in the cloud can build up areas of
positive and negative charge.
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LIGHTNING
The negative and positive charges repel each
other so the top of the cloud is positive and the
bottom of the cloud is negative.
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LIGHTNING
The negative charge at the bottom of the cloud
causes a positive charge to be induced on the
Earths surface.
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LIGHTNING
When the charge difference is great enough, the
air becomes a conductor, the electrons in the
cloud are transferred to the positively charged
ground.
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LIGHTNING

• Benjamin Franklin experimented with electricity.
  He discovered that sparks leave a sharply pointed
  object more readily than a rounded object.

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• He invented the lightning rod. It is a pointed
  rod that is attached at the top of a building and
  connected to the ground by a cable. It prevents
  a large build up of charge on the building.

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• Note Lightning tends to strike the highest point
  nearby so beware during a storm.

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COULOMBS LAW
Coulombs law states that for charged particles
the distance between the charges varies directly
with the product of the two charges and inversely
with the square of the distance between them.
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COULOMBS LAW
inverse relationship F d2 direct relationship
F, q1 q2) charge negative and/or positive
d
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COULOMBS LAW

• F Electric Force (N)
• q1 charge of 1st particle (C)
• q2 charge of 2nd particle (C)
• d distance between the two
• charges (m)
• k Coulombs constant
• (9 x 109 Nm2/C2)

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• http//virlab.virginia.edu/VL/Electrostatics.htm
• http//websites.kahoks.org/Richert_Gary/sciweb/ele
  ctric.htm