E/M Of Electron

Purpose

To demonstrate that the charge and the mass of electrons are quantized.◙

Equipment

E/M of electron apparatus, complete

Suggestions

NOTE: Apparatus may be damaged if operating instructions are not followed. Instructions are delivered with◙the apparatus.

Setup Time

One hour (must be obtained from labs).

Images

p2-31

Description

This is the classic lab apparatus. Electrons ejected from a hot filament are accelerated by a DC voltage and bent in circles by the magnetic field of a large pair of Helmholtz coils. The path of the electrons is visible due to interaction of the electron beam with residual nitrogen gas in the tube, which produces the characteristic blue glow.

References

Lecture Demonstration Instructions Sheet. ◙William J. Thompson, Determining e/m with a Bainbridge tube: Less data, more physics, AJP 58, 1019-1020 (1990).