Thomson Model of the Atom

Thomson’s plum‑pudding atom treats the atom as a uniformly charged sphere in which the enclosed positive charge grows with the cube of the radius. Inside this sphere the electric field increases linearly with distance, giving each electron a restoring force that follows Hooke’s law. The result is simple harmonic motion at a single frequency ω = √(Ne²/4πɛ₀mR³). Electrons also repel each other via the usual 1/d² Coulomb force, so the overall dynamics are a balance of a linear inward pull and mutual repulsion.

Students can set the number of electrons (N = 1–12), toggle radiation damping, and use the Irradiate button to launch a visible wave train that kicks the electrons. The Settle control lets the system relax, and a toggle shows emitted radiation. Electrons are draggable, allowing learners to displace a single electron and watch it oscillate and eventually settle into stable ring configurations.

Through this simulation students see how a uniform charge distribution creates a harmonic restoring force, explore the interplay of electrostatic attraction and repulsion, observe radiation damping effects, and understand why the Thomson model predicts a single spectral line, linking atomic models to observable spectra.