3B Scientific Air Cushion Plate - Handbuch (Seite 63)

Physical Experiments on the Air-Cushion Table
12
1.4. Instructions for Usage
The air-cushion table is placed onto the overhead
projector so that the arrow on the pressure cham-
ber points to the projection screen. The magnetic
barriers (fig. 1) are placed onto the air-cushion
table so that their numbers (no. 1 to no. 4) match
the markings at the edges of the experiment sur-
face. The magnetic barrier with the slit at the
bottom is arranged at the side of the table where
the tube of the fan connects. The air flows through
the slit and over the experiment surface when
activating the impulse valve.
The pressure chamber and the fan are connected
by the tube (fig. 2). The tube should run as straight
as possible. Only one position is possible when
connecting it to each of the devices. This is why
both ends of the tube and the connectors of the
devices are marked with a line. The tube is con-
nected to the device so that both lines meet. Then
it is turned slightly to the right or to the left.
Next, the experiment surface is aligned horizon-
tally by means of the adjusting screws at sides 2
and 4 by means of the spirit levels.
When needed, the impulse valve is pressed sev-
eral times for approx. 1 second. The fan has to be
set to a sufficient performance level, since other-
wise the pressure of the air cushion is too low
and the hover discs will sink onto the experiment
surface.
To install the lattice model, the holding device is
screwed onto the frame of the air-cushion table.
The lattice model is then inserted into the groove
of the holding device (fig. 3) The influence of
the lattice model on the motion of the hover discs
strongly depends on the height of the lattice over
the experiment surface. The holding device,
which is marked with a scale (fig. 4) can be infi-
nitely adjusted to the appropriate height using a
setscrew.
This allows for demonstrations of the behavior
of conductors, semi-conductors and insulators.
The electrodes are used to create an electric field.
They can be applied in two positions. Placing
them onto their base will create a gap between
the experiment surface and the electrodes. This
gap is large enough for the aluminum hover discs
to fit through. These are then charged in accor-
dance with the polarity of the respective electrode.
The electrodes can also be turned around so that
their bases point upwards. Then the aluminum
parts touch the experiment surface and the hover
discs contact the electrodes.
The voltage applied should be over 20 000 V.
When the voltage is lower, the electrodes have to
be arranged closer to each other.
An especially well-suited voltage source is the
electrostatic generator.
The influence of the electric field on the motion
of the hover discs can also be demonstrated by
slightly tilting the experiment surface. The de-
gree of inclination then corresponds to the
strength of the electric field.
The strength of the fan is adjusted until the hover
discs just begin to move freely. This ensures a
relatively low level of noise. When the airflow is
stronger, disturbance caused by the noise of the
fan cannot be avoided. For this reason, it should