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Coulomb equilibrium of charges

What you are seeing: four fixed charges (the squares) generate a 2D electrostatic potential. A test charge (the dot) you drag is repelled by like charges and attracted by opposite charges. Equilibria are the points where the local force vanishes; their stability is governed by ∇2V=0\nabla^2 V = 0 (Earnshaw: equilibria are saddles, never stable).

Figure 1. Drag the test charge to feel the field. Equilibrium at the center for symmetric configurations.
Q (corner)1.0
q (test)0.5
config
show field

WHAT TO TRY

  • Vary each control and watch the rail readouts respond.
  • Compare the diagnostic plot against the live scene.