PhysicsUKFields lab

ELECTRIC DEFLECTION

An electron between plates

0 nsReady

Choose an investigation

Experiment controls

Selected apparatus

Presentation & timing

Playback speed changes presentation time only. Transformer playback: 50 ms per screen second. Arrow lengths indicate direction, not a shared force/speed scale.

Setup changes are saved on this device. Reopening starts a fresh run.

Experiment notebook

Capture stores the readings, apparatus settings and live edits at that instant. Blank values mean unavailable. Captures stay in this session when you switch simulations.

Explore, measure, explain

Try it in class

  1. Predict the path or reading before pressing Run.
  2. Change one variable. Launch another particle or move the probe.
  3. Capture readings and use the graph or kept traces to compare.
  4. Explain the result using the field direction, charge and force.

Working on the bench

Drag an object to move it independently. Select a launcher and drag its direction handle. Drag either ruler endpoint. Use Edit for precise positions, strengths, speeds and directions. Measurements use world coordinates, so zooming never changes a reading.

Space: Run/Pause · L: Launch · C: Capture · arrows: move selection · Shift + arrows: fine move · Delete: remove · Escape: cancel placement · [ / ]: select previous/next object. These shortcuts apply when the bench is focused.

Reading the science

Front view shows x and y; z points towards you. Top view shows x and z. A dot means B towards you; a cross means B away. Blue arrows show velocity, amber arrows force. Particle dots and source radii are enlarged for teaching. Traces grow from calculated motion.

Alpha particles have +2e charge; β− is an electron and β+ is a positron. Their masses differ greatly. Changing particle species affects new launches. Existing particles retain their own properties.

Model assumptions

Three-dimensional relativistic test-particle motion follows F = q(E + v × B). Fixed sources superpose. Particles do not interact with one another or recoil against apparatus. Source charges are finite spherical shells. Plates have sharp ends, no fringing and infinite depth; potential outside their longitudinal span is unavailable. B regions also have sharp boundaries and infinite depth. Bar magnets use a smooth dipole approximation; wires are long straight uniform-current cylinders.

Sources and apparatus can be repositioned live. These manual edits are quasi-static: they do not model induced electric fields from moving magnets, radiation or mechanical work on sources. Use the transformer workspace for time-dependent induction. Plates, source spheres, slits and detector screens intercept flights; the open bench ends at ±1 m in each coordinate.

The transformer solves a common-flux linear core and resistive circuits. Steady DC gives no secondary emf; switch-on and switch-off do. This model omits saturation and heating and is a conceptual demonstration, not a transformer design calculator. Changing turns during a run is an idealised parameter edit.

Measurements & saving

The first field probe supplies the main E/B/potential readings; each additional probe labels its own tip. The main particle and graph show the most recently launched particle. Detector counts include all contacts. Ruler length is 3D; the protractor measures an angle in the displayed view. CSV contains SI values, full settings and live edits. Save setup preserves apparatus and transformer settings, not flights or notebook readings.

Keep trace stores the current trajectories as grey dashed comparisons. Restart clears flights, counts and live graph, while retaining apparatus, comparisons and captured readings. Clear traces removes paths without changing the motion. Undo/redo are available while paused and edit apparatus without rewinding time.

Physics & inspiration

OpenStax: magnetic forces and motion · OpenStax: transformers · PhET: Charges and Fields. Original PhysicsUK implementation and artwork.