# Ohm's Law and resistor calculation

Despription of the Ohm's Law definition and resistor calculation

## Ohm's Law

The Ohm's Law defines one of the most important rules for calculating electrical circuits.

In its original form, it determines the resistance in ohms from a current and voltage measurement when $$U$$ in volts and $$I$$ in amps are known

$$\displaystyle R=\frac{U}{I}$$           $$\displaystyle 1Ω=\frac{1V}{1A}$$

Calculation of current $$I$$, if $$U$$ in volts and $$R$$ in ohms are known

$$\displaystyle I=\frac{U}{R}$$           $$\displaystyle 1A=\frac{1V}{1Ω}$$

Calculation of the voltage $$U$$, if $$I$$ in amperes and $$R$$ n ohms are known

$$\displaystyle U=I· R$$           $$\displaystyle 1V = 1A· 1Ω$$

Example

Calculation of the resistance of a load at $$230$$ volts a current of $$4.5$$ amperes

$$U=230V$$
$$I=4.5A$$

$$\displaystyle R=\frac{U}{I}=\frac{230}{4.5}=51.1Ω$$