Models of Electricity
Scientists use observations
about nature to construct models
and theories to explain how nature
works.

These models can
change over time
when new
observations are
made.

This is what
happened to the
theory that explains
how electricity works.
 In
the 1600’s, 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.
 Benjamin
Franklin explained that positive
and negative charges were due to the
electric fluid.
 When
an object lost fluid it became
negatively charged, and when it gained
fluid it became positively charged.
 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.
 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.
 Then,
in 1897 J.J.
Thomson
discovered the
electron (which
you discovered, if
you recall, in the
chemistry unit).
 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.

Remember an atom is made up of a nucleus
containing protons and neutrons.
 The
nucleus has an overall positive
charge.
 Spinning around the positive nucleus are
electrons, which are negatively charged.
 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.
 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.
 Some
atoms hold their electrons loosely
while others hold on tight.