Simulation · Physics · Class 12
Which leads: V or I?
From the lesson AC through an inductor in Alternating Current. Change the values and watch what happens.
Which leads: V or I?Physics · Class 12
The idea behind it
NCERT §7.4
- For a pure inductor (negligible resistance), the loop rule gives v − L di/dt = 0, so di/dt = (vm/L) sin ωt.
- Integrating, i = −(vm/ωL) cos ωt = im sin(ωt − π/2), with im = vm/ωL. There is no constant term, because the source swings evenly about zero.
- The quantity ωL plays the part of resistance. It is the inductive reactance XL = ωL, measured in ohm, and im = vm/XL.
- XL grows in proportion to both the inductance and the frequency.
- The current lags the voltage by π/2, a quarter of a cycle: it reaches each maximum a quarter period after the voltage does.
- The average power into a pure inductor over a cycle is zero. Energy stored in its field during one quarter cycle is handed back to the source in the next.
- Example 7.2: a pure 25.0 mH inductor on 220 V, 50 Hz has XL = 2π × 50 × 25 × 10⁻³ = 7.85 Ω and an rms current of 220/7.85 = 28 A.