scientific
3
012-04046C
Current Balance and Accessory
Operation
Figure 3 Setting Up the SF-8607 Basic Current Balance
Magnet
Assembly
0.01 gram
Balance
Lab Stand
Current Loop
Main Unit
Figure 4 Connecting the Ammeter and Power Supply
Ammeter
0-5A (Max.)
Power Supply
Base Unit
F
orce, grams
Force vs. Current for SF-8607
0
1
2
3
4
1.36e-20
1.00e-1
2.00e-1
3.00e-1
C rrent amps
Current, amps
Figure 5 Typical Data for Force versus Current
Measurements
If you are using a quadruple-beam balance:
First measure the weight of the Magnet Assembly with
no current flowing (F
0
). Then turn on the current, adjust
it to the desired level, and measure the weight of the
Magnet Assembly with current flowing (F
I
). With
current flowing, the reading will be higher or lower than
before. The difference in weight (F
I
– F
0
) is proportional
to the force exerted on the magnetic field (and thereby
the magnets) by the current-carrying wire. To investi-
gate the relationship between current and force, vary the
current and measure the weight at each value.
If you are using a top-loading electronic balance:
With the Magnet Assembly sitting on the balance, tare
the reading by pressing the appropriate switch on the
balance. This subtracts the weight of the Magnet
Assembly from ensuing weight measurements, so only
the force caused by the current will be measured. Turn
the current on. If the reading is negative, reverse the
leads where they plug into the arms of the Main Unit.
The measured weight is directly proportional to the force
caused by the current moving through the magnetic
field.
Varying the Wire Length
Vary the wire length by using one of the six different
Current Loops. To change the Current Loop:
➀
Swing the arm of the Main Unit up, to raise the
present Current Loop out of the magnetic field gap.
Pull the Current Loop gently from the arms of the
base unit. Replace it with a new Current Loop and
The SF-8607 Basic Current Balance
To set up the Current Balance (see Figure 3):
➀
Mount the Main Unit on a lab stand having with a rod
3/8 inch (1.1 cm) in diameter or smaller.
➁
Select a Current Loop, and plug it into the ends of the
arms of the Main Unit, with the foil extending down.
➂
Place the Magnet Assembly on a balance with at least
0.01 gram sensitivity. Position the lab stand so the
horizontal portion of the conductive foil on the Cur-
rent Loop passes through the pole region of the mag-
nets. The Current Loop shouldn't touch the magnets.
Connect the power supply and ammeter as shown in
Figure 4.
Measuring the Force
➧
Note: In this manual, we use the balance reading
in grams as our measure of force. Most students
will realize that the mass reading is proportional to
the actual force, which is given by the equation
F = mg. If you wish to use the actual force value,
simply multiply each reading in grams by 0.0098
newtons/gram to arrive at a force in newtons, or by
980 dynes/gram to arrive at a force in dynes.
➃
