Electromagnetism
RLC off resonance
This preset drives below resonance: capacitive reactance dominates, so current leads voltage (φ < 0).
RLC off resonance — interactive physics simulation. This preset drives below resonance: capacitive reactance dominates, so current leads voltage (φ < 0). Free browser-based virtual physics lab with live SI measurements and a guided tutorial.
Off-resonance impedance
Below resonance, capacitive current leads voltage (φ < 0).
This preset drives below resonance: capacitive reactance dominates, so current leads voltage (φ < 0).
- Z > R off resonance
- φ ≠ 0
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
This RLC circuit is driven off-resonance (at half its resonant frequency), so its current lags or leads the driving voltage by a fixed phase angle. Does the instantaneous current still oscillate sinusoidally at the same frequency as the drive?
Predictions to weigh
- No — the current oscillates at a different frequency than the drive.
- Yes — the current oscillates at the exact drive frequency, just phase-shifted relative to the voltage.
- The current isn't sinusoidal at all in steady state.
Variable roles
What you set:
- Time t (s)
What you measure:
- Instantaneous current i(t) (A)
How the investigation runs
- Open the rlc-off-resonance preset and press Reset. R = 20 Ω, L = 1 H, C = 0.01 F, drive ω = 5 rad/s (half the resonant ω₀ = 10 rad/s), V₀ = 10 V.
- Enable the instantaneous-current readout.
- Read the instantaneous current at each listed time.
What the printable worksheet asks students to work out
- First compute Z = √(R² + X²) and φ = atan2(X, R) with X = ωL − 1/(ωC), using R = 20 Ω, L = 1 H, C = 0.01 F, ω = 5 rad/s (giving Z = 25 Ω, φ ≈ −0.64 rad). Then compute i(t) = (V₀/Z)sin(ωt − φ) using V₀ = 10 V. Compare to the table.
- The phase angle here is negative, meaning the circuit is capacitor-dominated at this frequency (below resonance). Explain what a negative φ means for whether the current leads or lags the driving voltage.
Where this shows up beyond the lab
- The current amplitude here (V₀/Z = 10/25 = 0.4 A) is smaller than it would be exactly at resonance (V₀/R = 10/20 = 0.5 A). Explain why driving an RLC circuit off-resonance always results in a smaller current amplitude than driving it at resonance.
- Because off-resonance frequencies produce smaller current amplitudes, an RLC circuit acts as a natural frequency filter. Explain why this circuit would respond weakly to a very high-frequency or very low-frequency signal mixed in with its resonant frequency.
- AP Physics 2 — Unit 12: Magnetism and Electromagnetism
- AP Physics C: Electricity and Magnetism — Unit 13: Electromagnetic Induction
- IB Physics — D.4 Induction
- General High School Physics — Magnetism & electromagnetism
- NGSS High School Physics — Electric current and magnetic fields
- Welcome to Rlc Off Resonance
- Select the RLC circuit
- Press Play
- Above or below resonance
- Open the Properties panel
- You did it!
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.