PURPOSE: To demonstrate visually the force on an electron beam by a magnetic field.

DESCRIPTION: A cathode ray tube produces a beam of electrons which can be seen as it hits a phosphorescent surface inside the tube. Holding a magnet close to the CRT parallel to the table so that it produces a horizontal magnetic field inside the tube causes the electron beam to deflect up or down. The vector nature of the force can be studied by reversing the magnet.

Click on the photograph above to see pictures of the effect.

SUGGESTIONS: See Question of the Week #58 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA 5H30.15)

EQUIPMENT: Cathode ray tube with power supply and weak bar magnet.

SETUP TIME: None.