## Sunday, May 6, 2012

### Charged Particles in B-fields

Here's a case of charged particle flying through magnetic fields, and what happens to those particles. We know that fundamentally magnetism is formed by moving charges. So the moving charged particle has its own magnetic field. This field interacts with any external magnetic field, thus creating a magnetic force. We know this goes as F = qv x B. It is a cross product. But this then means the force is perpendicular to the motion of the particle. The consequence of this condition is circular motion, or mv^2/R = qvB. This video will show ActivPhysics simulations to get a sense of the 3-D nature of this motion. If the particle comes in 90-degrees to the magnetic field, we get a circular orbit. If the particle comes in at any angle other than 90-degrees or 0-degrees (parallel) to the field, then there is a component of motion perpendicular to the field (circular motion), as well as a component parallel to the field, which means no force and it keeps moving in that direction. A spiral/helix/corkscrew results! I also show a simulation of a mass spectrometer, where we use the circular motion to measure the mass of particles or ions. Check it out.