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Formula: **Practical (Real) Voltage Source**

$$U = \frac{\class{blue}{U_0}}{1 + \frac{R_{\text i}}{R}}$$
$$U = \frac{\class{blue}{U_0}}{1 + \frac{R_{\text i}}{R}}$$
$$\class{blue}{U_0} ~=~ \left( 1 + \frac{ R_{\text i} }{ R } \right) \, U$$
$$R_{\text i} = \left( \frac{\class{blue}{U_0}}{U} - 1 \right) \, R$$
$$R = \left( \frac{\class{blue}{U_0}}{U} - 1 \right)^{-1} \, R_{\text i}$$

## Terminal Voltage

`$$ U $$`Unit

`$$ \mathrm{V} $$`

Electrical voltage of an ideal voltage source

*MINUS*the voltage across the internal resistance \(R_{\text i}\).It can be seen from the formula that the terminal voltage depends on both the internal resistance of the voltage source and the load resistance.

## Source voltage

`$$ \class{blue}{U_0} $$`Unit

`$$ \mathrm{V} $$`

Voltage of an ideal voltage source - by definition, it has infinite resistance.

## Internal resistance

`$$ R_{\text i} $$`Unit

`$$ \mathrm{\Omega} $$`

Resistance of a practical (real) voltage source.

## Load resistance

`$$ R $$`Unit

`$$ \mathrm{\Omega} $$`

Electrical resistance connected to the terminals (to which the terminal voltage is applied). The terminal voltage and source voltage are equal when the internal resistance is zero.