Physics · Alternating Current · NEET
No, but they play a similar role. Both are measured in ohms and both limit the current (current amplitude i_m = v_m / XL, just like i_m = v_m / R for a resistor). The big difference: a resistor turns electrical energy into heat, so it dissipates power. A pure inductor's reactance only stores and returns energy in its magnetic field, so its average power over a full cycle is zero. So XL controls the size of the current but wastes no energy.
XL = 2πfL, so XL is directly proportional to f. Physically, an inductor opposes any change in current by producing a back-emf (Lenz's law). Higher frequency means the current is changing direction faster, so the coil produces a larger opposing emf and fights the current harder. That is why XL grows as f grows.
The ohm (Ω), exactly the same as resistance. You can check with the formula: ω is in rad/s (i.e. 1/s) and L is in henry (H = Ω·s), so ωL = (1/s)(Ω·s) = Ω. This is a common one-mark NEET check.
Pure DC has frequency f = 0, so XL = 2πfL = 0. The current is steady and not changing, so there is no back-emf to oppose it. That is why an ideal inductor behaves like a plain wire (short circuit) for steady DC but limits current strongly for high-frequency AC.
Yes. XL = 2πfL is directly proportional to L. A larger coil (more turns, iron core) stores more magnetic energy and produces a stronger back-emf for the same rate of current change, so it opposes AC more. This is exactly why inserting an iron rod into a coil dims a bulb in series with it.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
XL = ωL = 2πfL, where L is the inductance in henry, f is the frequency in hertz, and ω = 2πf is the angular frequency. The result is in ohms (Ω).
XL = 2πfL = 2 × 3.14 × 50 × (25.0 × 10⁻³) = 7.85 Ω. RMS current I = V/XL = 220 / 7.85 = 28.0 A. This is the standard NCERT Example 7.2.
An ideal (pure) inductor consumes zero average power over a full AC cycle. It stores energy in its magnetic field during one quarter cycle and returns it during the next, so no net energy is lost as heat.
XL doubles, because XL is directly proportional to f. If XL was 7.85 Ω at 50 Hz, it becomes 15.7 Ω at 100 Hz, and the current halves for the same voltage.
In a pure inductor the current lags the applied voltage by a phase angle of 90° (π/2). The reactance sets the size of the current, while the 90° lag sets its timing — covered in the next concept.
