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electromotive force
current and
resistance
led to the postulation of the fundamental law in electricity: Ohm’s law.
Fig.2
Electromotive force (abbreviated
EMF
), usually called voltage (
V
), is the
force or pressure that moves electrons through a conductor. If electrons are
piled at one end of the conductor, and if there are fewer electrons at the other
end, the excess of electrons will flow toward the point of deficiency, i.e. the
current will flow through the conductor from the negative end to the positive
one. The unit of the electromotive force is the volt,
V
, named after the Italian
scientist, Alessandro Volta.
The flow of electrons from one end of the conductor to the other is not
always the same. On their way, they collide with atoms and molecules, atoms
and molecules oppose them and that property of the conductor is called electric
resistance. The greater the number of free electrons in the conductor, the lower
is its resistance.
Most metals are good conductors, but the resistance of a conductor does
not depend only on the material of which the conductor is made. It also depends
on the cross-section of the conductor. The greater the cross-section, the lower is
the resistance of the conductor. The third element is the length of the conductor.
The longer the conductor, the greater is its resistance. And at last, there is the
temperature of the substance. If the temperature of a metal wire is higher, the
resistance will be higher. The unit of the resistance is the ohm, Ω, named in the
honour of G. S. Ohm.
I
stands for intensity, strength or amount of current. It is, in fact,
determined by the number or quantity of electrons, which pass through the
cross-section of a conductor per unit of time. The intensity depends upon the
potential difference, and the resistance of the conductor. The greater the
potential difference, the larger the quantity of electrons flowing through the
conductor – the greater the resistance, the smaller the quantity of electrons. The
unit of the intensity is the ampere,
A
, named for a French scientist, André
