Formula: Ohm's Law Voltage Electrical Resistance Electric current

$$U ~=~ R \, I$$ $$U ~=~ R \, I$$ $$R ~=~ \frac{U}{I}$$ $$I ~=~ \frac{U}{R}$$

Rearrange formula

Voltage

$$ U $$ Unit $$ \mathrm{V} = \frac{ \mathrm J }{ \mathrm C } = \frac{ \mathrm{kg} \, \mathrm{m}^2 }{ \mathrm{A} \, \mathrm{s}^3 } $$

Voltage is a measure of how much charge of different sign is separated from each other. The voltage is always measured between two points of the conductor. It is not possible to measure the voltage at only one point of the conductor.

In order for an electric current $I$ to flow between two points on the conductor, positive and negative charges must be separated, that is there must be a voltage between these points. The mutual attraction of the opposite charges creates an electric current.

Electrical Resistance

$$ \class{brown}{R} $$ Unit $$ \mathrm{\Omega} = \frac{ \mathrm{kg} \, \mathrm{m}^2 }{ \mathrm{A}^2 \, \mathrm{s}^3 } $$

Electrical resistance is a measure of how strongly electrically charged particles (like electrons) are affected as they move through the conductor. The resistance depends on the material used for the conductor.

The Ohm's law is characterized by the fact that the resistance $R$ is constant! So it doesn't matter what voltage is applied, the current through the conductor will adjust so that the ratio $U/I$, that is the resistance, always remains constant.

At a current of $I = 0.1 \, \text{A} $ and a voltage of $ U = 10 \, \text{V}$, the resistance is $ R = 100 \, \Omega $.

Electric current

$$ \class{red}{\boldsymbol I} $$ Unit $$ \mathrm{A} = \frac{ \mathrm C }{ \mathrm s } $$

Electric current indicates how much electric charge flows through a conductor per time. The greater the electric current, the more charge flows through the conductor (more charged particles move through the conductor).

At a current of $1 \, \text{A}$ (1 amp), $1 \, \text{C}$ (1 coulomb) of charge flows through the conductor per second.

With a resistance of $R = 10 \, \Omega $ and a voltage of $ U = 1 \, \text{V}$, a current of $ I = 0.1 \, \text{A} $ flows.