RL Time Constant Calculator Formula
Understand the math behind the rl time constant calculator. Each variable explained with a worked example.
Formulas Used
Time Constant (τ)
tau = inductance * 1e-3 / resistanceTime Constant (ms)
tau_ms = inductance / resistanceVariables
| Variable | Description | Default |
|---|---|---|
inductance | Inductance(mH) | 50 |
resistance | Resistance(Ω) | 10 |
How It Works
RL Time Constant
The RL time constant governs how quickly current builds up or decays in an inductor-resistor circuit.
Formula
τ = L / R
After one time constant, the current reaches 63.2% of its final steady-state value.
Worked Example
A 50 mH inductor with a 10 Ω resistor.
- 01τ = L / R
- 02τ = 50e-3 / 10
- 03τ = 0.005 s = 5 ms
Frequently Asked Questions
How does the RL time constant differ from RC?
In an RL circuit, τ = L/R (inductance over resistance). In an RC circuit, τ = R*C. Both describe exponential approach to steady state.
Why do inductors resist changes in current?
A changing current creates a changing magnetic field, which induces an EMF that opposes the change (Lenz's law).
What happens when an inductive circuit is suddenly opened?
The collapsing magnetic field can induce a very large voltage spike. This is why flyback diodes are used to protect circuits with inductors.
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Open RL Time Constant Calculator