Electricity & magnetism lab

Drag charges and watch real traced field lines, push a magnet through a coil to induce current, and tune an R-L-C circuit to see its phasor diagram rotate.

Lessons

Pick a topic, read the steps, then try them right in the sandbox below.

Class 12 — Electric field and potential around charges

Concept: field lines point away from positive charges and into negative ones; potential is highest near a positive charge and lowest near a negative one, and both fall off with distance.

Switch to Electrostatics mode.
Drag the small grey probe close to a positive charge and note Field |E| at probe and Potential V at probe — both should be large.
Drag the probe far from both charges — both readings should shrink toward zero.
Flip one charge's sign (if a control is available) or drag the probe exactly between two equal-and-opposite charges — the field lines should visibly curve from the positive charge straight into the negative one.

Takeaway: field lines are a picture of force direction, while potential is a single number describing the "electrical height" at a point.

Class 12 — Electromagnetic induction and Lenz's law

Concept: moving a magnet through a coil changes the magnetic flux through it, and that changing flux induces an EMF: ε = −N dΦ/dt. The minus sign is Lenz's law — the induced current always opposes the change that caused it.

Switch to Induction mode.
Set an Oscillation freq. and watch the magnet swing through the coil. Watch Flux Φ rise and fall, and EMF ε=-NdΦ/dt spike each time the flux is changing fastest (as the magnet passes through the coil).
Note the Induced current direction flips depending on whether the magnet is approaching or receding — that sign flip is Lenz's law in action.
Raise Coil turns N and watch the EMF spikes grow taller for the same magnet motion.

Takeaway: EMF depends on how fast the flux changes, not on the flux itself — that's why the EMF peaks exactly when the magnet is moving through the coil, not when it's sitting still inside it.

Class 12 — AC circuits: impedance and resonance

Concept: in a series R-L-C circuit driven by an AC source, the inductor and capacitor's opposing reactances partly cancel, so total impedance Z = √(R² + (X_L−X_C)²) can be tuned by frequency — and there's one frequency where it's smallest.

Switch to AC circuit mode.
Set Resistance R, Inductance L and Capacitance C to fixed values, then sweep Frequency f up from low to high.
Watch Impedance Z — it should dip to a minimum at one particular frequency (resonance), where Peak current I₀ and Avg. power both hit their maximum.
Check Phase φ at that same frequency — it should be at (or very near) zero, meaning current and voltage are in step.

Takeaway: at resonance the inductor's and capacitor's reactances exactly cancel, leaving only the resistance to limit the current — which is why current peaks there.

What each mode covers

Electrostatics — drag either charge or the small grey probe. Field lines are traced, not decorative: each one starts at a charge and is stepped forward along the real Coulomb field direction until it reaches another charge or leaves the frame. The probe reads the actual field vector (magnitude + direction) and potential at its position.

Electromagnetic induction — the magnet oscillates through the coil; EMF is computed from the actual rate of change of flux, ε=−N dΦ/dt, not just "current flows when it's close." Watch the galvanometer flip direction exactly when the magnet switches between approaching and receding — Lenz's law in real time.

AC circuit — a series R-L-C driven by V=V₀sin(ωt). Impedance, phase angle and current all update live as you move the sliders, and the phasor diagram shows the actual angle between voltage and current — capacitive circuits lead, inductive circuits lag, exactly as the reactances dictate.

Idealisations: simulation units (k=1 for Coulomb's law), a smooth bell-curve flux model for the coil rather than a full Biot-Savart calculation, and steady-state AC analysis (no start-up transient) — the same honest-simplification spirit as every other lab in Forces.

Part of Forces — see Learn for the class 12 electrostatics, EMI and AC topics this maps to.

Test yourself

Pick Class 12 in the physics quiz to test yourself on electrostatics, current electricity, EMI and AC — 10 random questions, with an explanation for every answer.

Take the physics quiz →