Resistance vs Impedance

What is impedance

Impedance (Z)  is similar to Resistance (R) . Impedance and Resistance both oppose the current in the circuit. Both are almost the same thing, But resistance related to DC Circuit. Resistance opposes the steady electric current in the DC circuit. Resistance remains the same (constant) at any different frequency range.

Impedance is related to the AC circuit. Impedance varies according to changing the frequency, this is not constant at different frequency range. Impedance also includes reactance (Inductive and capacitive property of the circuit).

Reactance

Reactance is the Resistance produced to AC Currents by Inductors and Capacitors only. This is a measure of the type of opposition to AC electricity due to capacitance or inductance.

The impedance is denoted by Z and unit of it is Ohm (Ω).

If the level of ohm is higher then the level impedance is also higher.

Impedance = Resistance + Reactance (Either inductive or Capacitive or both)

In DC circuit, Impedance is an effective Resistance of the circuit.

Z= R

In AC circuits, it possesses both magnitude and phase, unlike resistance, which has only magnitude.

In the case of a capacitor, When the frequency increased then the resistance (Impedance) of the capacitor decreases. In Inductor this is just the opposite, When we increase the frequency range then Impedance increase in the inductor.

Impedance $Z=\frac{V}{I}$

Impedance is defined as a combination of resistance and reactance.

As we cannot assume any circuit with DC Current without Resistance, We cannot assume a circuit with AC current without Impedance.

Resistive Power– Energy burns by resistive power to Heat  goes through that system,

In Reactive Power- the energy goes to Antennas, Speaker,  transmission line, cable, etc represents how much energy to be stored and propagates. Not burn to heat ie Impedance.

Resistance  $R=\frac{V}{I}$   If there is Only Resistor is connected with Load in any circuit then is called Resistor.

• Reactance  $Z=\frac{V}{I}$     If any circuit there is Only inductor or capacitor connected with load. Then the value of v/I is called reactance.

In Reactance, There are 2 cases

(1)  If inductor in connected then in this case reactance is called inductive reactance,

and its value in scalar form  XL = ѡL,  and in vector form XL=JѡL  Where ѡ=2Πf.  Here If the frequency is increased then the value of wL is also increased.

(2) If Capacitor is connected then the Reactance is called Capacitive Reactance and it is denoted by (scalar form) Xc =$\fn_jvn&space;Xc=\frac{1}{C}$

In vector form $\fn_jvn&space;Xc=\frac{1}{j\omega&space;C}$   Where  $\fn_jvn&space;\omega&space;=\frac{1}{2\pi&space;fc}$  If frequency (f) is increased then the value of Xc is decreased.  ie ω inversely proportional to 2Πf.

♦  Impedance –  If Any circuit consists of Resistance Inductor. Or Resistance – Capacitor, Or Resistance-inductor-Capacitor. Then the value of v/I is called Impedance.

It is denoted by $Z=\frac{V}{I}$

• If Resistor(R) and Inductor(L) connected –The value of Impedance (scaler form) $Z=\sqrt{R^2+(L\omega&space;)^2}$

In vector form Z= R+jωL

• If Resistor (R) and Capacitor(C) connected –  Then

Impedance  $\fn_jvn&space;Z=\sqrt{R^2+(\frac{1}{C\omega&space;})^2}$

And In vector form impedance $\fn_jvn&space;Z=R+\frac{1}{j\omega&space;C}$

• If the Resistor (R), Inductor (L) capacitor (C) Connected – Then

Impedance   $\fn_jvn&space;Z=\sqrt{R^2+(L\omega&space;-\frac{1}{C\omega&space;})^2}$

In vector form   $\fn_jvn&space;Z=R+j\omega&space;L-\frac{1}{j\omega&space;C}$

Unit

• Impedance – Ω
• Reactance –  Ω
• Resistance – Ω