Chapter 20 Notes

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Chapter 20 Notes

• Static Electricity

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• Ben Franklins experiment in 1752
• Electrostatics-The study of electrical charges
  that can be collected and held in one place, in
  other words, they are AT REST

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Something about ATOMS

• Every atom has a positively charged nucleus
  surrounded by negatively charged electrons
• All electrons are identical (same mass and
  charge)
• Nucleusprotons and neutrons
• Atoms usually have an equal number of protons and
  electrons

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Charge

• Electrons are negatively charged
• Protons are positively charged
• The attracting and repelling is due to something
  called charge
• LIKE CHARGES REPEL
• OPPOSITE CHARGES ATTRACT

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Insulators

• Materials through which charges will not move
  easily
• Examples-glass, dry wood, plastics, cloth, dry air

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Conductors

• Materials, such as metals, that allow charges to
  move about easily. Charge spreads very quickly
  over the entire object
• Examples-door knob, desk, lightening rod

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Why are metals good conductors?

• Because at least one electron on each atom of the
  metal can be removed easily they move freely
  throughout the entire piece of metal
• Most of the time, the materials involved in
  Static Electricity are nonconductors of
  electricity

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Conservation of Charge

• Individual charges are never created nor
  destroyed
• The combined total charge of 2 interacting
  objects remains the same

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Things to Remember!!

• 2 Kinds of Electrical Charges-Positive Negative
• Charges exert force on other charges over a
  distance
• The force is stronger when the charges are closer
  together
• Like charges repel, Opposite charges attract

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How do we Charge Object?

• Conduction
• Charging a neutral object by touching it with a
  charged object

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• Induction
• Charging a neutral object by bringing it close to
  a charged object, causing a separation of
  charges, then removing the object to be charged,
  trapping equal but opposite charges

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Coulombs Law

• Says that the magnitude of a force between 2
  charges varies directly with the magnitude of the
  charges and inversely with the square of the
  distance of the charges
• FK(qq/d2)
• K is a constant
• K9.0x109 Nm2/coul2

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Electric Potential Energy

• Bodies with diff. concentrations of electrons
  have a difference in potential between them.
• This means that the 2 bodies are a source of
  potential energy.
• The difference in potential is measured in Volts
  (v)

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• Electrons flow from areas of higher conc. to
  areas of lower conc.
• An electron flow takes place if 2 bodies have a
  difference in potential and are connected by a
  conductor.
• This flow is called an electric current.

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• The way to maintain a current is to maintain a
  charge on the 2 bodies that are at diff.
  potentials.
• To maintain the potential, some devices must pump
  the electrons back to the body with higher
  concentrations as soon as they get to the lower
  concentration. These are called Voltaic
  Cells-Batteries.

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