Electrical engineering - Basics Page 10

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The following formula is used if the temperature of the conductor deviates substantially from the assumed constant temperature of 20C and if one has to determine the resistance exactly under these particular conditions:

Examples for different temperature coefficients
Temperature coefficient [1/K]
(Lord Kelvin of Largs, English Physicist, 1824-1907)
Copper 0,0039
Aluminium 0,0038
Iron 0,0045

1.6 Ohm's law

The three discussed physical units of measurement amperage, voltage and electrical resistance have a special relationship, i.e. they depend on each other. Georg Simon Ohm discovered the following mutual dependencies and expressed them in the so called Ohm's law:
  1. If one increases the voltage with the resistance remaining constant, the amperage is increasing with the same ratio the voltage is increasing.

  2. If one increases the resistance with the voltage remaining constant, the amperage decreases with the same ratio the resistance is increasing.
The following formula is used to describe these dependencies:

Voltage = amperage * resistance

The basic formula of Ohm's law can be transformed as follows:




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