Description of the relationship between impedance, reactance, capacitive reactance and inductive reactance

Impedance

In a circuit with resistance, inductance and capacitance (RLC circuit), the blocking effect on the alternating current is called impedance; the impedance is usually Z, the unit is ohm Ω; the impedance is composed of resistance, inductive reactance and capacitive reactance, but not three. For a specific circuit, the impedance is not constant, but varies with frequency; in a series circuit of resistors, inductors, and capacitors, the impedance of the circuit is generally greater than the resistance.

2. Reactance

The blocking effect of capacitors and inductors on the alternating current in the circuit is called reactance, expressed as X, and the unit is ohm Ω. The reactance changes with the frequency of the AC circuit and causes a phase change in the current and voltage in the circuit.

3. Relationship between impedance, reactance, capacitive reactance and inductive reactance

Impedance, the sum of resistance and reactance, is expressed mathematically as:

Z is the impedance, the unit is ohm Ω

R is the resistance in ohms Ω

X is the reactance, the unit is ohm Ω

j is an imaginary unit

When X > 0, it is called inductive reactance

When X = 0, the reactance is 0

Capacitive reactance when X <0

For an ideal purely inductive or capacitive reactance component with a zero resistance, the impedance strength is the magnitude of the reactance.

The total reactance of a typical circuit is equal to:

X = XL −Xc

Where XL is the inductive reactance of the circuit and Xc is the capacitive reactance of the circuit.

3.1 Sense resistance

Inductive reactance (XL) is generally due to the presence of an inductive circuit (such as a coil) in the circuit, and the resulting electromagnetic field produces a corresponding electrical force that blocks the flow of current. The greater the current change, that is, the larger the circuit frequency, the greater the inductive reactance; when the frequency becomes 0, that is, when it becomes direct current, the inductive reactance also becomes zero. Inductive reactance causes a phase difference between current and voltage. The inductive reactance can be calculated from the following formula:

XL = ωL = 2 × π × f × L

XL is the inductive reactance, the unit is ohm Ω

ω is the angular frequency in radians per second rad/s

f is the frequency in Hertz Hz

3.2 capacitive reactance

The concept of capacitive reactance (Xc) reflects the characteristic that AC can pass through the capacitor. The higher the AC frequency, the smaller the capacitive reactance, that is, the smaller the blocking effect of the capacitor. The capacitive reactance also causes a phase difference between the current and the voltage across the capacitor. The capacitive reactance can be calculated from the following formula:

Xc = 1/(ω×C)= 1/(2×π×f×C)

Xc is the capacitive reactance in ohms Ω

ω is the angular frequency in radians per second rad/s

f is the frequency in Hertz Hz

C is the capacitance in Farad F