CHARGE · CURVATURE · MAGNETIC FORCE
Charged particle in a magnetic field.
Launch it across the field for a circle. Add motion along the field for a helix.
Inside the magnetic field
B · magnetic fieldv · instantaneous velocityF · magnetic force
Left-drag rotates; right-drag pans the camera. Choose Place / drag particle to move its starting position. Scroll or pinch to zoom. Use 3D view to re-centre.
One force. Three possible paths.
The magnetic force is perpendicular to velocity. It changes the direction of motion while speed and kinetic energy stay constant. A velocity perpendicular to B gives circular motion; adding a parallel component gives a helix. Motion exactly along the field stays straight.
For a negative charge, the middle finger points opposite to velocity. In a helical path, the guide uses the perpendicular component of that direction; the main velocity arrow shows the full velocity.
Model and field boundary
The outlined cube contains a uniform magnetic field. The particle starts inside it. On leaving the cube it continues in a straight line with zero magnetic force. The sharp boundary is an idealisation; fringe fields, gravity, electric fields, collisions and radiation are omitted. Speeds are limited to 5 × 10⁶ m s⁻¹ so this classical model remains well below the speed of light. Motion is slowed for viewing; the time display reports physical time.
Charge is in elementary charges e; mass is in atomic mass units u. Changing a setup control resets the launch. The radius, period and pitch describe the circular/helical motion inside the field, even after the particle exits.
Hand model: “Left Hand Rule” by mHafiz0809, CC BY 4.0. Adapted for orientation and display.
Explore charged-particle motion in a magnetic field
Launch a positive or negative charge into a uniform magnetic-field region. Adjust charge, mass, speed and field direction; compare circular, helical and straight paths. Pause or scrub time to inspect instantaneous velocity, magnetic force and the rotating left-hand guide.
Supports magnetic-force and charged-particle-motion topics in IB Physics, A Level Physics, AP Physics 2 and AP Physics C: Electricity and Magnetism. This classical model conserves speed and kinetic energy; outside the idealised field boundary the particle continues along a straight tangent.