*Resistance* is an ideal electric circuit component, which is characterised by energy losses in a circuit as heat, some mechanical work, or electromagnetic radiation.

Resistance is marked with that letter *r*, and it’s measurement unit is Ohm. It is an ideal electric circuit component, where the irreversible process of electromagnetic energy absorption goes. Mathematically explained:

$r=\frac{u}{i}$

The eqation above is called Ohm’s Law. R always has a positive value. Another characteristic

$g=\frac{1}{r}$is called conductance, and is measured with Simens (sim).

*Instantaneous power*, on the resistor, is the following:

${P}_{r}=u*i=r*{i}^{2}=g*{u}^{2}$

Here you see how instantaneous power is related to voltage and conductivity.

Generally speaking voltage on the resistor is related to current which goes through the resistor.

$U=I*R$This relation is known as volt-ampere characteristic. *I* general, it is not linear.