Models of Electricity

1
Models of Electricity

• Scientists use observations about nature to
  construct models and theories to explain how
  nature works.

2

• These models can change over time when new
  observations are made.
• This is what happened to the theory that explains
  how electricity works.

3

• In the 1600s, the theory to explain how
  electricity was called the one-fluid model.
• William Gilbert suggested that electricity was a
  fluid that could flow between objects.

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• Benjamin Franklin explained that positive and
  negative charges were due to the
  -------------------.
• When an object lost fluid it became negatively
  charged, and when it gained fluid it became
  positively charged.

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• Over time the theory changed because off new
  observations.
• The two-fluid model of electricity was suggested.
  This model used two types of fluid instead of
  just one.

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• One of the fluids was thought to be positively
  charged while the other was negatively charged.
• An object could gain a positive charge by either
  gaining positive fluid or losing negative fluid.
• An object could gain negative charge similarly.

7

• Then, in 1897 J.J. Thomson discovered the
  electron (which you discovered, if you recall, in
  the chemistry unit).

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• This meant that the model of electricity had to
  be changed again, to pretty much what we use now.
• This is called the particle theory of
  electricity.

9

• Remember an atom is made up of a nucleus
  containing protons and neutrons.

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• The nucleus has an overall positive charge.
• Spinning around the positive nucleus are
  electrons, which are negatively charged.

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• The particle model of electricity states that
  when two objects are rubbed together, electrons
  are removed from the atoms of one object and move
  to the second object, it becomes negatively
  charged.

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• The first object is positively charged because it
  is missing some electrons.
• Nothing in the nucleus moves.
• Negatively charged electrons move, while positive
  charges are stuck where they are.

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• Some atoms hold their electrons loosely while
  others hold on tight.