Reactance and Impedance, Types of Reactance, Wattless Current (For CBSE, ICSE, IAS, NET, NRA 2022)

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Reactance and Impedance

Reactance

  • It is essentially the inertia against the motion of electrons in an electrical circuit that is the attribute against the flow of electrons in an electrical circuit.
  • Denoted by the symbol R
  • It is measured in units of the Greek symbol ohm.
  • It is mathematically the ratio of the potential difference V and the current flows between two points in that circuit, In an electrical circuit.

  • It is also known as the imaginary resistance of an electrical circuit. The motion of electrons constitutes current generation in an electrical circuit and any inertia against this motion of electrons constitutes reactance.
  • It is generated due to the element՚s inductance or capacitance.
  • It resists the change in current of the element, whereas in an electric field it resists the change in voltage of the element, In a magnetic field
  • It is mathematically represented by the letter X and has its unit of measurement in the form of the Greek symbol ohm.

Types of Reactance

  • Capacitive reactance
  • Inductive reactance

Capacitive Reactance

  • When a capacitor is connected to a circuit with AC supply, there is no simultaneous change in the capacitor voltage and capacitor current.
  • The potential difference across the capacitor is dependent on the AC power supply.
  • Current is maximum when the potential difference is at zero.
  • The capacitive reactance for a capacitor with capacitance C connected in the circuit along with AC power supply is given as:

Where,

  • is the capacitive reactance
  • f is the frequency of AC power supply
  • C is the capacitance

Inductive Reactance

  • The current across an inductor changes when potential difference develops across it, in inductive reactance.
  • The potential difference and rate of change of current are proportional to each other.
  • The inductive reactance for an inductor with inductance L connected in the circuit along with AC power supply is given as:

Where,

  • is the inductive reactance
  • L is the inductance of the inductor
  • f is the frequency of the alternating current

Difference between Reactance and Resistance

Difference between Reactance and Resistance
ParameterResistanceReactance
Variation of currentIt is a property of an electrical component which opposes the flow of currentIt is a property of an electrical component which opposes the change in current
Power dissipationleads to power dissipationIt does not lead to power dissipation
Denoted byResistance is denoted by RReactance is denoted by X

Impedance

  • It is a combination of resistance and reactance.
  • Essentially, it is anything and everything that obstructs the flow of electrons within an electrical circuit.
  • So, it affects the generation of current through the electrical circuit.
  • It is present in all the possible components of the circuit and across all possible electrical circuits. Impedance is mathematically symbolized by the letter Z and has its unit as ohm.
  • It is a superset of both resistance and reactance combined.
  • In phasor terms, impedance Z is represented as a combination of resistance R and reactance X as:

Where reactance X is a combination of Inductive XL and capacitive Xc

Wattless Current

  • Component of the AC current that consumes zero power in a circuit is known as a wattless current.
  • So, the average power dissipated in a AC circuit is given by the equation

  • From equation, the average power dissipated not only depends on voltage and current but also on the cosine of the phase angle between them.
  • In a circuit that contains only a capacitor or inductor, the phase difference between the voltage and current is .
  • So, becomes zero and the power dissipated will be zero.
  • There will be no power dissipation in spite of the current flowing in the circuit.
  • This current which results in no power dissipation is referred to as wattless current.

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