When electrons are separated from atoms
– either through friction (eg, static electricity),
chemical reaction (eg, a battery), electromagnetism or
other phenomenon – an electrical field is formed,
consisting of two oppositely charged terminals, and an
associated “tension” or “pressure” between them.
The measure of this “tension” or
“pressure” is known as voltage.
Voltage is also known as the difference in
electrical potential, since it is a measurement of the potential of
the electric field to induce an electric current in a conductive
material. In other words, it is the force responsible for
“pushing” or “pulling” electrons through a conductive material.
Given equal resistances, higher voltage results in a more powerful
electric current.
If charge is a measure of the amount of electrons,
then voltage is a measure of the electrical force that this amount
can exert. For example, in a battery, the terminals contain charges
(negative and positive), but the actual voltage exists in the space
between the terminals.
Mathematically, voltage (V) is electric potential
energy per unit charge, measured in joules (0.7376 ft-lbs) per
coulomb (6.25 x 1018 electrons), or more commonly, volts.
Therefore, a 9V battery can produce 9 joules of energy per coulomb.
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In a hydraulic analogy, voltage is often (loosely)
compared to water pressure.
In the diagram on the left, tank B has more
pressure than tank A due to the higher water level. In the
same way, a 9V battery has a higher “electrical pressure” than a
1.5V battery.
Current is a measure of electrical charge in motion. Consider a copper wire, connected to the terminals of a battery (-Q and +Q)  |
Once contact is made between the wire and the battery terminals, electrons from the negatively-charged terminal (on the left) repel the free electrons from the atoms in the copper wire. At the same time, electrons on the right are attracted to the positively-charged terminal. The result is electrical current - a chain-reaction of electrons drifting through the wire.
Mathematically, current (I) is expressed in amperes (A), where
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