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1. Safety instructions
All the components of the instrument are safe to work
with, provided that they are used in accordance with
instructions and regulations.
The transformer core, yoke and pole shoes should be
handled carefully to avoid the risk of injuries resulting
from their considerable weight.
In experiments involving a strong magnetic field, do
not allow any ferromagnetic materials to come near
the instrument, as they would be powerfully attracted
towards it with a risk of damage or injury, for example
through trapping of fingers.
Equipment that is to be connected to the mains must
be checked for any damage before it is used.
2. Description
The Langensiepen current balance is used for experi-
ments on electrodynamics and Lorentz forces and
involves measurements in which the force on a con-
ductor in a magnetic field is balanced mechanically.
3. Equipment supplied
1 Stand with agate cup bearings for balance beam
1 Balance beam with pointer and terminals for cur-
rent connections
1 Set of conductor loops
1 Coil, 5 turns
1 Pointer for zero calibration
1 Hydrodynamic friction brake
2 Special connecting leads
1 Bottle of glycerine (250 ml)
2 Drive weights, 100 g and 200 g
1 Counterweight weight
2 19 g weights
1 Reel of nylon thread
1 Instruction sheet
1 Transformer core with yoke and fixing clamp
1 Pole shoes set
2 100 g weights
1 200 g weight
2 Coils, 600 turns
1 Storage block
1 Dynamometer, 0.1 N
10 Spacer rings
4.1 Generating a strong magnetic field
Fig. 1
The strong magnetic field generator is assembled as
shown in Figure 1 using the following components
from the accessories set U8496818: U-core (19), two
coils (20), pole shoes (27).
The connecting leads chosen must be long enough to
ensure that they do not cause any mechanical ob-
struction to the operation of the current balance.
The pole shoes (27) are placed on the core (19) without
any special fixing. They rest in place securely enough
under their own weight, and when the field is applied
they are held more firmly. The distance between the
pole shoes is determined by the choice of spacer rings
(23), giving a separation of 10, 15 or 20 mm when
used singly, or 25, 30, 35 or 40 mm by combining
them. The field between the pole shoes is approxi-
mately uniform.
It is recommended that a stabilised DC power supply
U33020 is used as the voltage source for excitation of
the magnet (see Fig. 3). When switching the field on or
off, the large inductance of the system must be taken
into account by avoiding switching a large current.
The following table contains some guideline data on
the magnetic flux density B that can be generated
with different values of the coil current and spacing of
the pole shoes. The magnet set-up consists of the U-
core with two 600-turn coils connected in series.
Pole shoe
1 cm
separation
Excitation
Flux B
current
2 A
0.18 T
1 A
0.13 T
0.5 A
0.06 T
2
4. Operation
2 cm
Flux B
Flux B
0.15 T
0.12 T
0.09 T
0.07 T
0.04 T
0.03 T
3 cm
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