Chains with R, C, L elements

Electrical circuit with R-element


Pic.1

Consider a circuit with an R-element, as shown in Figure 1. Place the directions of current and voltage and write down the electric equations of this circuit according to Ohm’s law:

i = u / R = (Um / R) sin (ωt + ψu) = Imsin (ωt + ψi)

it is obvious that Um = RIm; ψu = ψi, then the phase angle between voltage and current will be 0, i.e.
φ = ψu - ψi = 0, which corresponds to the time diagram shown in Figure 1, the voltage and current coincide in phase.
For valid values ​​Ohm's law: U = RI




the impedance of the resistive element is always a valid positive number, which is equal to the active resistance value R.

Power on R-element:

phase angle φ = 0, then P = UIcosφ = UI, Q = UIsinφ = 0, therefore, the total power on the resistive element is equal to the active power. This means that the resistor is working to convert electrical energy into heat.