RL Circuit: An Inductor Resists Sudden Current Changes

1 · Predict

An inductor and resistor are connected to a 10 V battery. Does current jump instantly to its final value, or does it ramp up gradually like a charging capacitor's voltage?

• Current ramps up gradually, following the same kind of exponential approach as an RC circuit's voltage.
• Current jumps instantly to E/R.
• Current oscillates before settling.

2 · Set Up

1. Open the rl-circuit preset and press Reset. R = 10 Ω, L = 1 H, giving a time constant τ = L/R = 0.1 s; the battery supplies 10 V.
2. Enable the inductor-current readout.
3. Press Play and record the inductor's current at each listed time.

3 · Collect Data

Plot inductor current I (y-axis) against time t (x-axis) for your three readings. Does the curve flatten out as it approaches 1 A?

4 · Analyze

1. For one trial, compute I = (E/R)(1 − e^(−t/τ)) using E = 10 V, R = 10 Ω, τ = 0.1 s. Compare to the table.
2. Explain why an inductor's current ramp-up (RL circuit) follows the same mathematical shape as a capacitor's voltage ramp-up (RC circuit), even though the two components store energy completely differently.

5 · Extend

1. An inductor's defining behavior is opposing any CHANGE in current (not opposing current itself, the way a resistor does). Explain why, right at t = 0, the current must start at exactly 0 A even though the battery is fully connected.
2. When a current-carrying inductor's circuit is suddenly broken (switch opened), the inductor tries to maintain its current, which can create a large voltage spike (this is how spark plug ignition coils work). Explain why interrupting an inductor's current path is more dramatic than interrupting a resistor's.

The Physics Behind This Experiment

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