3B SCIENTIFIC PHYSICS 1000913 Instructions D'utilisation page 7

Experiment 2
•
Set up the equipment as in experiment 1,
but add a 50 mm convex lens between the
spectral lamp and the heater so that a
slightly converging beam passes thorough
the tube.
•
Carry out the experiment as described above.
Within this beam it is possible to see a bright
resonance fluorescence. When it is totally dark,
it is possible to see weak secondary radiation
outside the beam.
Explanation: excited sodium atoms emit reso-
nance radiation uniformly from all sides. For this
reason, atoms outside the beam can also be
excited to resonate.
5.2 Absorption of sodium light from a spec-
tral lamp
Additionally required:
Semi-transparent paper, stand equipment
•
Set up the sodium spectral lamp about 50
behind the heater so that the light illumi-
nates the heater from the rear and emerges
from the viewing window in the panel at the
front.
•
Suspend a sheet of semi-transparent paper
from a stand in front of the heater so that it
is parallel to the front window to use as a
viewing screen.
•
Carry out the experiment as described in
section 5.1
Now the tube appears as a shadow in the light
from the spectral lamp between two bright strips
of light.
The primary sodium light is almost totally ab-
sorbed inside the sodium fluorescence tube. By
contrast, direct light that passes uninterrupted
through the heater between the window and the
tube appears on either side of the tube's
shadow.
Fig. 2 Absorption of sodium light
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5.3 Observation of D line in white halogen
Additionally required:
1 Hand spectroscope with Amici prism 1003531
1 Experiment light, halogen
1 Transformer, 12 V, 60 VA (230 V)
or
1 Transformer, 12 V, 60 VA (115 V)
1 Converging lens on rod, 50 mm
2 Stand bases
•
•
A sharply defined yellow line (D line) appears in
the spectrum. By slightly varying the position of
the spot of light on the tube (letting it shine
through the tube at a slight angle), the propor-
tion of the light reflected can be increased,
which causes the D line to become even more
conspicuous.
5.4 D line as a dark feature in white halogen
•
•
•
Observation of the extremely fine line (Fraun-
hofer line) requires a bit of practice. It is impor-
tant that a red beam is already visible inside the
tube in the focus of the halogen lamp. The oper-
ating temperature of the tube should between
240° and 250°.
Subject to technical amendments
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light
Set up the optical lamp and the convex lens
behind the heater in such a way that the
light forms a beam as narrow as possible at
the point where it is projected upon the so-
dium fluorescence tube. The spot of light
should shine through the tube either just
above or just below the metallic reflector.
Use the hand spectroscope and observe the
spot of light that emerges through the win-
dow at the side.
light
Line up the optical lamp and the convex lens
as described in section 5.3.
Set the heater to 250°C.
Use the hand spectroscope and view the
light passing through the tube from the front.
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