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•
Carefully adjust the fine setting using the fre-
quency selector knob seeking out a peak in the
signal between about 1 ms to 1.5 ms in width.
Note:
When looking for the peak, it can be helpful to
loosen the knurled screws a bit to change the
strength of the magnetic field and thus the signal.
•
Vary the frequency to bring it to the middle of
the peak and write down what that frequency is.
•
Carry out the experiment again with different
material samples.
For the polystyrene sample (green top) the frequency
will be in the same range as for the glycerine sample.
For the Teflon sample (blue top) the frequency will
be lower (see Figs. 9 to 11).
Another experiment can be carried out in which the
stalk of a plant can be inserted into the sample
chamber for its resonant frequency to be deter-
mined.
Fig. 8 Experiment set-up featuring NMR unit with an oscilloscope
6.5 Evaluation
Resonant frequencies of material samples
1
Glycerine (
H)
1
Polystyrene (
H)
19
Teflon (
F)
1
Plant stalk (
H)
The following therefore applies:
ν
=
ν
Glycerine
Polystyren
e
ν
40
.
06
=
Teflon
ν
42
.
58
Glycerine
4
42.58 MHz/T
42.58 MHz/T
40.06 MHz/T
42.58 MHz/T
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