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Set voltage switch U to ON. Set up a voltage
U at which the oil drop slowly rises past a
selected initial scale marking in the top part
of the measurement cell.
Move switch U to OFF so that the oil drop
starts to descend again.
Set switch t to ON as soon as the oil drop
has returned to the first position you chose.
This starts the measurement of time t
Set switch U to ON as soon as the drop
passes a selected scale marking in the
lower part of the measurement cell, thus
causing the drop to start rising again.
Measurement
of
measurement of time t
Set switch t to OFF as soon as the oil drop
has returned to the first position you chose.
This causes the measurement of time t
stop.
Set switch U back to OFF.
Read off the times t
voltage U ("Previous Voltage") from the
display and make a note of them along with
the separation of the scale markings.
Repeat the measurement for as many
different oil drops as possible and using a
variety of capacitor voltages. Change the
sign of the voltage U as you do so.
8.3 Correction for Stokes friction
Very small radii r
are of the same order of
0
magnitude as the mean free path of air
molecules. This requires a correction for the
Stokes force of friction. The corrected radius r
and charge q are then given by:
2
A
A
2
r
r
where
0
4
2
b = 82 m·hPa = constant, p: air pressure
1,5
A
.
q
q
1
0
r
r
is given by equations (2) or (5) and q
0
equations (3) or (6).
3B Scientific GmbH ▪ Ludwig-Erhard-Str. 20 ▪ 20459 Hamburg Germany ▪ www.3bscientific.com
.
2
time
t
stops
and
2
starts automatically.
1
to
1
and t
as well as the
1
2
b
A
(7)
p
(8)
by
0
Subject to technical amendments
© Copyright 2022 3B Scientific GmbH
8.4
Parameters relevant to the results
Temperature, air pressure and viscosity of air
are measured or calculated with the help of
built-in sensors and are displayed on the
screen.
Density of oil:
877 kg m
-3
at 15°C
-3
871 kg m
at 25°C
Density of air:
1.293 g m
-3
at 0°C and 1013.23 hPa
8.5 Evaluation
The charges of the oil drops can be
determined using equation (8).
The charges derived from measurement are
divided by a whole number n such that the
resulting values have the least possible spread
around their average, which represents an
estimate of the elementary charge of electrons
or protons. Standard deviation provides a
measure of the spread. The result is more
meaningful
the
more
recorded, i.e. the greater the size of the sample
and the fewer the number of values of charge
on the oil drops (recommendation: n < 10).
9. Storage, cleaning and disposal
Keep the equipment in a clean, dry and
dust-free place.
Before cleaning the equipment, disconnect
it from its power supply.
Do not clean the unit with volatile solvents
or abrasive cleaners.
Use a soft, damp cloth to clean it.
The packaging should be disposed of at
local recycling points.
Should
you
need
dispose of the equipment
itself, never throw it away in
normal domestic waste. If
being
used
in
private
households
it
can
disposed of at the local
public
waste
disposal
authority.
Comply with the applicable regulations for
the disposal of electrical equipment.
measurements
are
to
be
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