RL Time Constant (τ = L/R on Rise)

Step the voltage on a series RL. Record i(t) and fit ln(1−i/i∞) vs t; slope = −1/τ, τ = L/R.

School· 22 min·Related simulator: RL Circuit

Goal

Find τ from i(t) = I∞(1 − e^(−t/τ)) using ln(1−i/I∞) = −t/τ + const.

Rise of current: 1−i/I∞ = e^(−t/τ) ⇒ y = ln(1−i/I∞) is linear in t with slope −1/τ.

Current rise; I∞ = 0.1 A in this model.

t (s)t = 0.0010

№	Time t s	Current i A	ln(1−i/I∞)
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Add at least 2 measurements to compute the fit.

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Generated: 27 Apr 2026, 02:36

Find τ from i(t) = I∞(1 − e^(−t/τ)) using ln(1−i/I∞) = −t/τ + const.

#	Time t (s)	Current i (A)	ln(1−i/I∞)
No measurements yet — take your first reading.

Add at least 2 measurements to compute the fit.

The RL time constant matches L/R within tolerance.

PhysSandbox virtual lab — values come from your session; add your own discussion of error sources.

The RL time constant matches L/R within tolerance.