KLINGER KSCIFBCD User manual

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Force Between Conductors KSCIFBCD
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FORCE BETWEEN CONDUCTORS DEMONSTRATOR
FBCD01
DESCRIPTION
A basic property of electromagnetism is the mechanical force which exists between two
neighboring, current-carrying conductors. This was first observed by Oersted in June of
1820 and was rapidly investigated by him as well as by Ampère, Biot and Savart, so
that
the theory was developed by the end of the same year. The unit of current, the Ampère,
is defined in terms of this force. However, observing the small force with simple
conductors requires large currents. The Force between Conductors Demonstrator offers
a simple, direct method for accomplishing this usually difficult and often unsatisfying
demonstration. The device consists of a metal frame (1, Figure 1), which supports two
long straight conductors that can pivot about vertical axes (2). The base of the frame
(3) contains a power supply to energize the conductors. Binding posts (4) allow voltage
to be applied to the conductors in various configurations. A pushbutton (5) applies the
voltage, allowing a large current to flow momentarily in the conduct
ors. Two adjustable
indicator arrows (6) show the direction of the current in each conductor. The movement
of the conductors indicates the generation of a magnetic force between them.
OPERATING INSTRUCTIONS
AND SUGGESTED ACTIVITIES
1
4
2
3
5
6
4
Figure 1

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SPECIFICATIONS
Conductors: Thin wall brass tubes with copper end pieces
Length: 39.5 cm
Diameter: 4.4 mm
Lever arm: 2.5 cm
Cold resistance (each): Approx. 0.013Ω
Power: Input: 110VAC/60Hz, 345W (max., - operate for < 5 seconds)
Output: Open circuit voltage 4.0V d.c., operating voltage 0.5—
1.5 V d.c.
Approx. operating currents: 55A in series, 2 x 37A in parallel
Fuse: Miniature fuse, 5 x 20 mm, 250V/3A
Dimensions: Height 56.5 cm, base diameter 19 cm, base height 8.5 cm
Weight: 4.25 kg
Connecting cords: 2 x 11 cm, 1 x 80 cm, spade lug connectors both ends
SAFETY
· The apparatus connects to a 110VAC outlet via a grounded plug. Observe all usual
electrical safety precautions when operating. In particular:
· Do not use the apparatus if the cord or plug is damaged.
· Do not use the apparatus in a wet or damp environment.
·
Do not defeat the grounding, which protects the user against dangerous external voltages
in case of internal damage to the circuitry.
· Make all changes to the connections with the apparatus unplugged from the 110VAC
outlet.
· Only operate the apparatus under responsible supervision by a technically qualified
person.
·
In use, the apparatus generates only low external voltages but very large currents, so the
conductors quickly become hot. Since the demonstration requires only seconds to
observe, there is no need for a prolonged operation. Do not operate the apparatus
continuously for more than about 5 seconds. Do not touch the hot conductors until they
have cooled (a few seconds)
BACKGROUND
A schematic diagram of two conductors carrying
currents i1and i2is shown in Figure 2. If we
consider short elements of the conductors ds1
and ds2 a distance r apart, then Ampère (and
others) showed in a series of careful
experiments that the force dF1which the
element ds2exerts on ds1is given by:
dF1= (μ0i1i2/4πr3).[ds1G
G
(ds2G
G
r)] (1)
where μ0is a constant.
But at a place where the magnetic induction is
B, a current-carrying element ds1experiences a force dF which can be expressed simply
by:
dF = i1.(ds1G
G
B) (2)
Comparing equations (1) and (2), we can view the force on ds1as generated by an
induction dB2created by the current i2in ds2. Then dB2would be given by:
dB2= (μ0/4πr
3
).i2.(ds2GGr) (3)
Figure 2

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The magnetic field His related to the induction Bin free space by the equation:
B= μ0H(4)
It turns out that μ0is the same constant discovered in equation (1), so by substitution
dH2= (i2/4πr3).(ds2G
G
r) (5)
which is the well-known Biot-Savart Law for the magnetic field of a current element. Note
that the strength of the field falls off as the inverse square of the distance from the
element.
Referring again to Figure 2, we can see that if ds1and ds2are parallel to one another,
the forces dF1and dF2are directed along rand will be equal in magnitude but opposite
in sign. Each conductor can be regarded as experiencing a force due to the magnetic field
of the other. Also, the forces between two parallel currents in the same direction are
attractive, which is the opposite of electrostatic charges and magnetic poles, where like
entities repel.
DEMONSTRATION
Preparation
Check that the pointed ends of the conductors and the
dimpled bearing contacts (see Figure 3) are clean and free
of oxidation. If necessary, gently clean them by rubbing
with a rough cloth.
·Insert the pointed ends of the conductors into the dimples in
the top and bottom bearing contacts and check that the
conductors swing freely. If they are too stiff or if they are not
held by the bearing contacts, gently bend the copper end pieces
until the fit and swing are satisfactory.
·Place the apparatus where the demonstration is to be made and
level it by adjusting the three threaded feet under the base until
the conductors remain in any position and show no tendency to
swing together at any point.
·Using the connecting cords supplied, connect one of the circuits
shown below and adjust the indicator arrows on each support
pillar to show the current direction in each conductor.
·Plug the apparatus into a 110VAC outlet.
Figure 3a
Figure 3b
Parallel connection
Currents upwards
Parallel connection
Currents downwards
Antiparallel connection
Currents clockwise

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Demonstration
Position the conductors so that the lever arms are approximately parallel.
·Keeping the hands well away from the conductors and contacts, press and hold the red
pushbutton. The green indicator light between the two binding posts on the top of
the base will illuminate to indicate that voltage is applied, and the conductors will
immediately move either together or apart, depending on the mutual directions of
the currents in each.
·DO NOT HOLD THE PUSHBUTTON DOWN FOR MORE THAN 5 SECONDS TO AVOID
EXCESSIVE GENERATION OF HEAT IN THE CONDUCTORS AND THE TRANSFORMER.
·Insulating boots at the ends of the conductors prevent metallic contact between the
tubes and a consequent short circuit in the case where the conductors move towards
each other.
·Unplug the apparatus from the 110VAC outlet and connect a different circuit for a
further demonstration.
MAINTENANCE
·The Force Between Conductors Demonstrator needs no special
maintenance except for the possible replacement of a burned-
out fuse.
·The fuse will burn out in the case of an accidental short circuit
between the supply binding posts due to an incorrect circuit
connection or if the pushbutton is held down for an excessive
time.
·The fuse is located on the bottom of the base (see Figure 4).
Unplug the apparatus from the 110VA outlet before unscrewing
the fuse cap. Replace the fuse with a 5 x 20 mm miniature fuse
rated at 250V/3A. DO NOT USE A HIGHER-RATED FUSE to avoid damage to the
apparatus.
·Store the apparatus in a cool, dry place away from sunlight.
COPYRIGHT NOTICE
This FBCD01 Force Between Conductors Demonstrator Operating Instructions and Activity Guide is
copyrighted and all rights are reserved. Permission is granted to all non-profit educational
institutions to make as many copies of this work as they need as long as it is for the sole purpose of
teaching students. Reproduction of this work by anyone for any other purpose is prohibited.
© United Scientific Supplies, Inc., 2009
Figure 4