PASCO SE-9638 e-m APPARATUS User Manual
Page 9
4
e/m Apparatus
012-03471E
®
where:
V = the accelerating potential
a = the radius of the Helmholtz coils
N = the number of turns on each Helmholtz coil = 130
μ
0
= the permeability constant = 4þ x 10
-7
I = the current through the Helmholtz coils
r = the radius of the electron beam path
Deflections of Electrons in an Electric
Field
IMPORTANT: Do not leave the beam on for long
periods of time in this mode. The beam will
ultimately wear through the glass walls of the tube.
You can use the deflection plates to demonstrate how the
electron beam is deflected in an electric field.
1.
Setup the equipment as described above for measuring
e/m except:
a. Flip the toggle switch to ELECTRICAL DEFLECT.
b. Do not supply current to the Helmholtz coils.
c. Connect a 0-50 VDC power supply between the
banana plug connectors labeled DEFLECT PLATES
(UPPER and LOWER).
2.
Apply the 6.3 (VDC or VAC), or voltage noted on tube,
to the HEATER and 150-300 VDC to the ELEC-
TRODES of the ELECTRON GUN (the accelerating
potential). Wait ten minutes to warm up the cathode.
3.
When the electron beam appears, slowly increase the
voltage to the deflection plates from 0 V to
approxmately 50 VDC. Note the deflection of the
electron beam. Note that the beam is bent towards the
positively charged plate.
Two Simple Demonstrations
1.
Instead of using the Helmholtz coils to bend the electron
beam, you can use a permanent magnet to show the
effect of a magnetic field on the electron beam. Just
provide the following power to the e/m apparatus:
HEATER: 6.3 (VAC or VDC), or voltage noted on tube
ELECTRON GUN ELECTRODES: 150- 300 VDC
When the electron beam appears, use your permanent
magnet to bend the beam.
2.
The socket for the e/m tube is designed so that the tube
can be rotated 90 degrees. The tube can therefore be
oriented so it is at any angle, from 0-90 degrees, with
respect to the magnetic field from the Helmholtz coils.
By setting up the equipment as for measuring e/m, you
can rotate the tube and study how the beam deflection is
affected.