Cyclotron Motion
Fire a charge into a uniform magnetic field, perpendicular to its velocity — adjust the entry speed, field strength, and charge-to-mass ratio to see the radius and period of the resulting circular orbit.
Preview — sign up free to change the numbers yourself
What you can adjust
- Entry speed
- 1 – 50 m/s
- Magnetic field (B)
- 0.2 – 5 T
- Charge-to-mass ratio (q/m)
- 0.2 – 10 C/kg
The particle's speed as it enters the field, perpendicular to it. A magnetic force does no work, so this speed never changes.
Stronger field means a tighter circle: r = v / ((q/m)*B) — try dragging it up and watch the radius shrink.
Both the radius and the period only ever depend on charge and mass through this one ratio.
About this simulation
What it shows
A charged particle enters a uniform magnetic field at right angles to its motion and travels in a circle. The radius and the time for one lap are read out.
The key idea
The magnetic force always points sideways to the motion, so it bends the path without changing the speed. The radius is r = v / ((q/m) B) and the period is 2π / ((q/m) B), which does not depend on speed.
Try this
Double Magnetic field (B) from 2 T to 4 T: the circle's radius halves, from 2.5 m to 1.25 m, and the period halves too, while the speed stays the same.