SACE Stage 2 Physics — Electricity & Magnetism 2.4

Charged Particle in a Uniform B Field

A charged particle entering a region of uniform magnetic field follows a circular arc of radius r = mv / |q|B. The Lorentz force F = qv × B always acts perpendicular to the velocity, so the speed is constant — only the direction changes.

Units

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Charge sign

Mass m

Speed v

Field strength B

Particle

Speed v

× 10⁶ m/s

Field strength B

Field direction

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Radius r = mv / |q|B —

Period T = 2π m / |q|B —

|F| = |q|vB —