This chapter covers electric phenomena when there is steady currentSteady current flow. CurrentCurrent comes from a movement of electric chargeElectric charge, and the continuity equation of currentContinuity equation of current holds generally based on the principle of conservation of chargePrinciple of conservation of charge. We need to apply an electric potentialElectric potential difference, i.e., a voltage, to a material to transport a currentCurrent through it. It is well known that Ohm’s lawOhm’s law holds empirically, which assumes a proportional relationship between the voltage and the currentCurrent. Its proportional constant, the electric resistanceElectric resistance, is proportional to the resistivityResistivity, which is a parameter inherent to the material. When there is steady currentSteady current flow, the energy, which is continuously supplied by an electric power sourceElectric power source, is dissipated. Kirchhoff’s lawKirchhoff’s law, used in direct currentCurrent electric circuits, is derived.