As we very frequently encounter with these terminologies when we go through the basic electrical circuit concept, so let’s understand definition one by one-
Resistance(R)
Resistance is a material property which opposes the flow of current to some extent in a material. When we apply a potential difference across the conductor then it encourages the flow of current but resistance present in the material provides a hindrance to the flow of current due to which overall flow of rate of charge decreases. Resistance is represented by the symbol “R” and it is measured in the unit of ohms (Ω)
Reactance(X)
Similar to resistance, Reactance also opposes the flowing of current when we apply alternating voltage source across it. This reactance is due to either inductor or capacitor element present in the circuit, Represented by symbol “X” and its SI unit is (Ω). But Reactance differ in several ways from resistance-
- Resistance is constant for all frequency values, It has only magnitude with no phase.
- The resistance value is always positive
- Reactance value depends on the frequency of supply voltage, it has both magnitude & phase.
- Reactance value is either positive or negative.
- Reactance store energy in the form of either magnetic field(for inductor) or electrostatic field(for capacitor).
- Capacitive Reactance is inversely proportional to frequency therefore for higher frequency reactance value goes down & vice-versa. Calculated by the below formula- Xc = 1/jωc = 1/j2πfc Where: Xc = capacitive reactance in (Ω) f = frequency in Hertz(Hz) C=Capacitance in farad (F)
- Inductive Reactance is directly proportional to frequency therefore for higher frequency reactance value goes up & vice-versa. calculated by the below formula- XL = jωL = j2πfL Where: XL = is inductive reactance in (Ω) f= frequency in Hertz(Hz) L = Inductance in henry(H)
Impedance (Z)
As we already understand the concept of resistance & reactance so when we combine resistance & reactance together we get Impedance(Z). It also opposes the flow of current when alternating voltage source applies across the circuit. So overall impedance is complex in nature and represented by Z= R+jX 
- It has two-dimensional quantities, the real part represented as resistance and imaginary part represented as reactance.
- It is a frequency-dependent quantity
- It has both magnitude and phase
- It is represented by the symbol (Z) & SI unit is (Ω).