Place positive and negative charges on a field, trace the electric field lines and equipotential surfaces, and verify Coulomb's law.
Add two Charged Body objects to the canvas. Set the left body to charge q₁ = +2 μC and the right to q₂ = −2 μC, separated by 4 m. Enable the Electric field overlay (E key). Field lines should appear flowing from + to −.
Place a small test charge (q = +0.1 μC, mass = 0.001 kg) between the two fixed charges at various distances r from q₁. Read the force from the body panel. Plot F vs 1/r² — you should get a straight line through the origin, confirming F ∝ 1/r².
Enable the Potential overlay. Equipotential lines appear perpendicular to field lines everywhere. Move a test probe along a line of constant colour — confirm the potential V = k·q/r stays constant. Equipotentials close to a charge are nearly circular.
Change q₂ to +2 μC (both charges now positive). Observe the field pattern — lines now emerge from both charges and the field is zero exactly midway between them. The test charge placed at the midpoint experiences zero net force (unstable equilibrium).
Remove the fixed constraint on q₂. With opposite charges, release q₂ and watch it accelerate toward q₁ under Coulomb attraction. Measure the acceleration at several positions and verify a = F/m = k·q₁·q₂/(m·r²). Compare the measured trajectory to what you'd predict analytically.
Discussion
Questions, corrections, and insights welcome.