Description

The Fine Beam Tube is used for investigating
the deflection of cathode rays in a uniform
magnetic field produced by a pair of 300mm
Helmholtz coils. In addition, it can also be used
for quantitative determination of the specific
charge of an electron e/m. Located inside a glass
bulb with a neon residual gas atmosphere is
an electron gun, which consists of an indirectly
heated oxide cathode, a Wehnelt cylinder and
a perforated anode. The gas atoms are ionised
along the path of the electrons and a narrow,
well-defined, luminescent beam is produced.
Incorporated measurement marks facilitate a
parallax-free determination of the diameter of
the circular path of the beam deflected in the
magnetic field. The Fine Beam Tube is mounted
on a base with coloured connectors. In order
to protect the tube, a protective circuit is built
into the base, which shuts off any voltage in
excess of the base’s pre-set cut-off voltage. The
protective circuit prevents excessive voltages
from damaging the heater filament and ensures a
“smooth” switch-on response once the voltage is
applied. Requires a 0-300V d.c. power supply and
300mm Helmholtz coils.