Direct Current

$$I=\frac{Q}{\Delta t} \quad Q=ne$$

Terminal voltage $$U=\frac{W_{ext}}{Q}$$

Interior voltage $$u=\frac{W_{int}}{Q}$$

Electromotive voltage $$E=\frac{E_{gen}}{Q}$$

$$E=U+u$$

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

$$R=\rho \frac{l}{S}$$

$$\rho$$ - resistivity

Drift velocity$$V_A=\frac{I \mu}{N_A \rho e S}$$

$$\rho=\rho_0 (1_\alpha \Delta t)$$

$$I=\frac{E}{R+r}$$

Kirchoff's laws

$$\sum_{k=1}^n I_k=0$$

$$\sum_{k=1}^n E_k=\sum_{i=1}^m I_ir_i$$

Resistors in series $$R_s=\sum_{k=1}^n R_k$$

Resistors in parallel $$\frac{1}{R_p}=\sum_{k=1}^n \frac{1}{R_k}$$

Star-triangle transformation

$$R_a=\frac{R_1R_2}{R_1+R_2+R_3}$$

Wheatstone bridge

$$R_x=R_4\frac{R_2}{R_1}$$