This simulator injects one charged particle into an ideal evacuated chamber where a pair of deflection plates produces a uniform electric field Ey and a pair of coils produces a uniform magnetic field Bz, both perpendicular to the particle's initial velocity. Field arrows show the applied directions independently of the charge; the particle's actual path reveals the combined Lorentz force those fields exert on it.
• A real-time 3D beam chamber with a source and focusing aperture, parallel deflection plates, magnetic field coils, an exit detector screen, gold electric-field and violet magnetic-field arrows, and an enlarged particle with teal (electric) and orange (magnetic) force vectors — with home view, focus-selected-part, auto-rotate, expand and toggleable labels. • Four live controls: initial kinetic energy (500–2000 eV), electric field Ey (−20 to 20 kV/m, positive upward), magnetic field Bz (−2 to 2 mT, positive +z) and charge sign (−1 electron or +1 an ideal positive test particle of the same mass). • Nine live metrics: x and y position, speed, kinetic energy, electric force Fy, magnetic forces Fx and Fy, the Ey value that gives a straight beam at the current speed, and the magnetic-only cyclotron period. • A Curves & measurements tab charting electric and magnetic forces and particle kinetic energy, the full model equations and snapshot measurements. • An Experiments tab with four guided scenarios (electric deflection, magnetic-only curvature, balancing the crossed fields, reversing the charge), a model-verification bench of independent automated checks, and a timestamped event log with a copyable trial report. • A Learn & assess tab with guided lessons, a two-question knowledge-check quiz and a written scope/reference statement.
The gold and violet arrows are the applied fields — they exist independently of whatever charge happens to be moving through them. The force on the particle is F = q(E + v × B): reversing the charge sign leaves the field arrows exactly as they were but reverses both the electric and magnetic forces at the same velocity. The electric force qEy does real work as the particle deflects, so kinetic energy changes; the magnetic force q(v × B) is always perpendicular to velocity and does zero work, so a magnetic field alone changes the particle's direction — curving it into a circle at the cyclotron period 2πm/|qBz| — without ever changing its speed or kinetic energy.
When Ey and Bz are both active and the particle enters along +x, the electric force qEy and magnetic force −qvₓBz act in opposite directions. They exactly cancel when Ey = v0Bz — the classic velocity-selector condition — letting the beam pass through nearly straight regardless of charge sign at that one specific speed. Away from that balance point, whichever force is larger dominates and the beam bends. The simulator's balance experiment sets this condition precisely so you can verify the beam runs straight at roughly 18.755 Mm/s.
No. The magnetic force q(v × B) is always perpendicular to the particle’s velocity, so it does zero work — magnetic power F·v is always zero in this model. A magnetic field changes the particle’s direction, curving its path into a circle, but its speed and kinetic energy stay exactly constant.
Nothing — the applied electric and magnetic fields are prescribed independently of the test charge, so the gold and violet field arrows stay exactly the same. What reverses is the force on the particle, since both the electric force qE and magnetic force q(v × B) contain the charge q directly.
It means setting the electric field so that Ey = v0Bz for the particle’s initial speed v0. At that specific balance, the electric force qEy and magnetic force −qv0Bz cancel exactly, so the beam travels through the chamber nearly straight — this is the same principle used in a physical velocity selector.
It is a nonrelativistic, single-particle model in an ideal evacuated chamber: no relativistic corrections, radiation, space charge, plate fringing fields or particle collisions are included, and motion is confined to the x-y plane. The positive-charge setting uses electron mass with reversed sign rather than a proton or a real positron source, so results are an educational approximation rather than beamline design calculations.