Free Charge Moving in Uniform Magnetic Field

• Since the magnetic force always acts at right angles to the charges motion, the magnetic force can do no work on the charge. The B-field cannot speed up or slow down a moving charge; it can only change the direction in which the charge is moving.

• The general path of a moving charge in a constant magnetic field is that of a helix with its axis parallel to the direction of the magnetic field.

• If you stand in such a way that you are looking directly into the oncoming magnetic field, the a positively charged particle will be seen to rotate in clockwies circle where as a negatively charged particle will rotate in counterclockwise circle. See Charge Particle moving in a Uniform B-Field IP Simulation..
• The component of velocity of the charged particle that is parallel to the magnetic field is unaffected, i.e. the charge moves at a constant speed along the direction of the magnetic field.

• If the particle has a component of velocity parallel to the magnetic field, then its circlular motion will drift at a constant speed (equal to that of its parallel-velocity component, vll) along the magnetic field producing an overall helical motion.
• The component of the velocity perpendicular to the magnetic field, is what cause the particle to executes uniform circular motion perpendicular to the magnetic field.

• The radius of the circular can be found by equating the magnetic force on the charge with the centripetal force.
 B-Field is into Paper
• Negatively charged particles circulate in the opposite direction as positively charged particles. The direction can be found using the right-hand-rule applied to the perpendicular component of the velocity. See Charge Particle moving in a Uniform B-Field IP Simulation.

• The angular frequency w at which a charged particle revolves about the magnetic field (normally called the cyclotron frequency) is independent of the speed of the particle.