Moving charges in a magnetic field

Electron Beams

• The path of the electronbeam can be seen whereit over the fluorescentscreen in the tube. Thebeam is deflected down-wards when a magneticfield is directed into theplane of the screen.

Electron Beams (Continued)

• Each electron within the beam experiences a force due to the magnetic field.

• The beam follows a circular path because the direction of the force on each electron is perpendicular to the direction of motion of the electron and to the field direction.

Calculating the Force

• A beam of charged particles crossing a vacuum tube is an electric current across a tube.

• F = BQv

(where F= the force of the particle

B= the flux density

Q= the charge of the particle

And v= the velocity of the charged particle.)

The use of Magnetic Fields

• Magnetic Fields are used in particle physics detectors in order to separate different charged particles and to measure their momentum from the curvature of the tracks they create.

• All charged particles which follow this curvature path is acted upon by a force due to the field. Positively charged particles (such as protons) are pushed in the opposite direction to negatively charged particles (such as electrons).