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The goal of this experiment is to observe and measure quantization
of electron energy levels in the Franck-Hertz experiment.
Electrons are accelerated through a thin gas of Neon and Mercury
from a hot filament towards a collection electrode. As the current
applied to the filament is increased, the electron velocities
increase, increasing the current across the gas potential barrier.
However, the electrons suffer energy loss via collisions with the
Neon and Mercury gas molecules. The object is to adjust the filament
current so that the electrons cause collisional excitation of the
gas molecules. This is observed by the subsequent deexcitation,
and spectral line emissin of the gas molecules. As a result of these
collisions, the accelerated electrons are unable to reach the collection
electrode and the current across the barrier drops sharply.
At left is the Franck-Hertz apparatus. The tube is filled with a
thin gas of Neon and Mercury. The filament at the bottom is used to
accelerate electrons towards the collection electrode near the
center of the tube. As the electron energies begin to collisionally
excite Neon, a faint purple glow appears near the collection electrode.
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