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Inductive reactance is denoted by
R
XL
XC
Z
XL
Quick Summary: Inductive reactance ($X_L$) is the opposition offered by an inductor to the flow of alternating current. It is measured in Ohms ($\Omega$) and is directly proportional to the frequency of the supply and the inductance of the coil.
Inductive reactance (XL) is the opposition offered by an inductor to the flow of alternating current. It is measured in Ohms (Ω) and is directly proportional to the frequency of the supply and the inductance of the coil.
XL=2πfL — The formula for inductive reactance where f is frequency and L is inductance.
XL=ωL — The angular frequency representation where ω=2πf.
When an AC current flows through an inductor, it creates a time-varying magnetic field, which induces a back electromotive force (EMF) according to Lenz's Law. This back EMF opposes the change in current, manifesting as an opposition to the flow of current known as inductive reactance. Unlike resistance, it does not dissipate power as heat but stores it in the magnetic field.
Inductive reactance increases linearly with frequency (XL∝f).
For DC circuits (f=0), XL=0, meaning an inductor acts as a short circuit in steady state.
The unit of XL is Ohms (Ω).
Inductive reactance causes the current to lag the voltage by 90 degrees in a purely inductive circuit.
Used in filters to block high-frequency signals.
Essential in designing chokes and transformers.
Causes phase lag between voltage and current.
Reactance values change with supply frequency, making it sensitive to harmonic distortion.
Low-pass filter circuits.
Induction motors and transformers.
Ballasts for fluorescent lighting.
Option A (R) represents Resistance, which is the opposition to both DC and AC.
Option C (XC) represents Capacitive Reactance, defined as 1/(2πfC).
Option D (Z) represents Impedance, which is the total opposition to current flow in an AC circuit, calculated as Z=R2+(XL−XC)2.
B is correct — Inductive reactance is denoted by the symbol XL and represents the frequency-dependent opposition of an inductor to AC current.
Remember that XL is directly proportional to frequency, whereas XC is inversely proportional to frequency; this is a classic trap in resonance and filter questions!