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Basic O'hms Law

Print Karnaugh 3 variables tables
Voltage V - [Volt]  V
Current I - [Ampere]  A
Resistance R - [Ohm]  Ω
Power P - [Watt]  W
V [Volt],    A [Ampere],    R [Ohm],    P [Watt]
The electrical resistivity  is also equal to the electrical field strength E [V/m] divided by current density J [A/m2]:
Current is the time change (derivative) of the charge:

Ohm's law states that a voltage across the element is directly proportional to the current through it.
The voltage is:       where     is the current in ampere and    is the resistance of the element and is measured in Ohm [] .
The resistance of an electrical conductor is directly proportional to its length  , inversely proportional to its cross sectional area , and a function of the material of which the conductor is made,
this is expressed in the simple formula:

The resistance of the conducting material is also dependent upon the temperature of the material. It can be shown experimentally that the resistance     of a conductor at the centigrade temperature   , in terms of its resistance   at temperature   , is given by:

  is the temperature coefficient of resistance (see table below).
In solid homogeneous materials the current density at any point is proportional to the electric field and depends only on the material of the conductor, that is:

Coulomb's Law: Two stationary electric charges repel or attract one another with a force proportional to the product of the magnitude of the charges and inversely proportional to the square of the distance between them.
Nomenclature
E -  Magnitude of electric field [V/m]
J -  Magnitude of the current density [A/m2]
R -  Electrical resistance [ohm]
-  Length of the conductor [m]
A -  Cross sectional area of the conductor [m2]
-  Charge in coulomb [C]
-  Conductivity of the material [A/Vm]
-  Electrical resistivity [Vm/A]
Material Resistivity ρ
[Ω • m]		 Temperature
coefficient per
degree 1/K		 Conductivity σ
x 107 [Ω • m]-1
Aluminium 2.65· 10-8 0.0039 3.77
Brass 6.4· 10-8 1.56
Cadmium 1.59· 10-8 6.29
Chromium 125· 10-9 0.08
Cobalt 6.24· 10-9 16.03
Copper 1.68· 10-8 0.004 5.95
Gold 2.21· 10-8 0.0037 4.52
Iron 9.61· 10-8 0.0057 1.03
Lead 2.08· 10-7 0.0039 0.45
manganese 4.8· 10-7 0.0000021 0.207
Mercury 9.8· 10-7 0.0009 0.10
Nickel 6.93· 10-8 0.006 1.44
Platinum 1.06· 10-7 0.00393 0.943
Silver 1.59· 10-8 0.0061 6.29
Tin 1.09· 10-7 0.0045 0.92
Titanium 4.20· 10-7 0.24
Tungsten 5.28· 10-8 0.0045 1.79
Zinc 5.90· 10-8 0.0037 1.69