Table of contents 1. Direct Current2. Ohm's Law3. Alternative Current4. Effective Value5. Phase Difference6. Impedance7. Ohm's Law for AC8. Power9. Three-Phase Direct Current Analogy between the potential difference or the voltage and difference of water level of which static pressure results can be made. The pressure will enable a water flow. In the same way, the voltage will enable a flow of electrons called current. If the liquid is more viscous than water, it will be harder for it to flow. Morever, its circulation will as more difficult as pipes’ cross sectional area is low. The circuit will have a certain resistance to the flow. The same phenomenon occurs in electricity: an electrical resistor opposes the flow of current. When the current circulates only in