Electrodynamics

Some basic electrical formulas - from my college time notebook

$\boxed{I=\frac{\Delta q}{\Delta t}}$   $\boxed{U=\frac{A}{q}}$ $\boxed{P=\frac{A}{t}}$   $\boxed{P=U·I}$   $\boxed{1kW·h=3.6·10^6J\\ 1J=\frac{1}{36}·10^{-5}kW·h\\ \left({SI}\right)E\left({kW·h}\right)=UIt·\frac{1}{36}·10^{-5}\left({kW·h}\right)}$

$\boxed{C=\frac{\Delta q}{\Delta U}}$   $\boxed{R=\frac{U}{I}}$   $\boxed{R=\rho·\frac{L}{A}=\frac{\rho·L}{\pi·r^2}}$   $\boxed{R_T=R_{T_0}\left({1+\alpha·\left({T-T_0}\right)}\right)}$

$$\displaystyle{\begin{array}{rlrlrl}I & =\ \frac UR & \quad R & =\ \frac UI & \quad U & =\ I·R\\ P & =\ U·I & \quad U & =\ \frac PI & \quad I & =\ \frac PU\\ P & =\ I^2R & \quad I & =\ \sqrt{\frac PR} & \quad R & =\ \frac P{I^2}\\ P & =\ \frac{U^2}R & \quad U & =\ \sqrt{P·R} & \quad R & =\ \frac{U^2}P\end{array}}$$

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$$\displaystyle{X_L=2\pi fL\\ X_C=\frac1{2\pi fC}}$$ $${}_{IF}\ X_L=X_C\ {}_{THEN}\ :$$ $$\displaystyle{f=\frac1{2\pi\sqrt{LC}}\\ L=\frac1{{\left({2\pi f}\right)}^2C}\\ C=\frac1{{\left({2\pi f}\right)}^2L}}$$

see also :

• Dynamic Formulas for the Capacitor and for the Inductor
• RC time constant