Physics Home > Teaching Labs > Electricity & Magnetism > Electron Gun

Topics

Points of Emphasis

Prerequisites

Lab Activities

Using a homemade electron gun, students do the following:

a. measurement of the mean free path of an electron vs the pressure in the gun; by plotting the data the students confirm that P is proportional to 1/L and from the slope of the line the ra-dius of an air molecule can be computed;

b. qualitative observation of the motion of an electron in an electric field;

c. qualitative observation of the magnetic focusing of a divergent electron beam in a uniform magnetic field when the beam is directed parallel to the direction of the magnetic flux lines; measurement of the electron velocity and the cyclotron frequency;

d. measurement of the charge to mass ratio for the electron; and

e. qualitative observation of a plasma.

All quantitative results are of order of magnitude agreement only.

Course Level

Introductory

Student Handouts

Equipment

Number of set-ups available: 1 Per lab station: 1 vacuum pump/hose 1 main power supply 1 light/e-gun platform 1 ruler 1 flashlight 1 circle template 1 black backdrop 1 high voltage power supply 1 36" red banana lead 1 black electrical deflection lead 1 right angle copper tubing/thermocouple 1 set of Helmholtz coils/leads 1 Helmholtz coil power supply 1 C-clamp 1 electron gun/filament shield Per class: 1 vernier caliper 1 accelerating anode from an e-gun 1 dead gun rack

Notes

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