Electrical engineering - Basics Page 9
Diagram 13: Factors that influence the electrical resistance
The above mentioned four factors
have the following effects on the electrical resistance:
In order to be able to better
and faster compare the effects of the factors of influence on the conductor resistance,
the resistivity [Rho]
has been defined for materials. The resistivity of a material refers by definition
to a conductor length of 1m, a conductor cross section of 1mm2 and a temperature
of 20°C (Anders Celsius, Swedish physicist, 1701-1744). With the help of the resistivity
r one can determine the total resistance R of a conductor according to the following
- The longer the conductor
is, the higher is the conductor resistance since the electron movements are
obstructed more the longer the distance is the electrons have to go.
- The smaller the conductor
cross section is, the higher is the conductor resistance since also fewer
empty positions are available in the grid.
- The smaller the number
of free electrons is and the bigger the obstruction by foreign atoms that
exist in the metal grid is, the higher is the conductor resistance since fewer
electrons can flow and those that can flow are being obstructed.
- The higher the conductor
temperature is, the higher is the conductor resistance since the atom oscillations
are getting bigger which leads to an obstruction of the electron flow.
for different resisitivities
( * mm2)/m