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When an electric charge is at rest it is spoken of as "static
electricity," but when it is in motion, it is referred to as an
"electric current." In most cases, an electric current is described
as a flow of electric charge along a conductor. To make an electron
current flow continuously along a wire, a continuous supply of
electrons must be available at one end and a continuous supply of
positive charges at the other. This is like the flow of water through
a pipe: to obtain a continuous flow, a continuous supply of water
must be provided at one end and an opening for its escape into some
receptacle at the other. The continuous supply of positive charge at
the one end of a wire offers a means of escape for the electrons. If
this is not provided, electrons will accumulate at the end of the
wire and the repulsion back along the wire will stop the current
flow.
The rate at which the free electrons drift from atom to atom
determines the amount of electrical current. In order to create a
drift of electrons through a circuit, it is necessary to have an
electrical pressure, or "voltage." Electric current, then, is the
flow of electrons. The more electrons in motion, the stronger the
current. In terms of automotive applications, the greater the
concentration of electrons at a battery or generator terminal, the
higher the pressure between the electrons. The greater this pressure
(voltage) is, the greater the flow of electrons.
In modern electric car designs, the drive motors are often used as
the brakes also, allowing them to switch over into performing as
generators, which charge the batteries with the energy generated.
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