Download The Measurement of a Magnetic Field in Fundamental Units

The Measurement of a Magnetic Field in Fundamental Units
FB = Fg
By:
10/15/2012
Submitted to Mr. Spangler in partial fulfillment of the objectives for A. P. Physics:
III. ELECTRICITY and MAGNETISM
D. Magnetostatics
INTRODUCTION
The magnetic force on a current carrying wire is, F = BIL where L is the length of the section of a U- loop
perpendicular to a magnetic field and is the current flowing through the loop.
OBJECTIVES
1. In this experiment we shall determine the magnitude of the magnetic field in the center of a long coil of
current-carrying wire, a solenoid.
2. The purpose of this experiment is to measure magnetic fields in more fundamental units, using the fact that a
magnetic field exerts a force on a current-carrying wire. If we measure the force F in Newtons, the current I in
ammeters and the length of the wire L in meters the strength of the field provided the wire is perpendicular to
the direction of the field.
MATERIALS USED
1. Air core solenoid current balance
2. 2 ammeters (0 — 15 ampere)
3. 2 DC power supplies
4. Connecting wires
5. Fine sandpaper
6. String
EXPERIMENTAL SETUP
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L Is the only part of the U- loop that is significant, because It along is perpendicular to the magnetic field.
EXPERIMENTAL PROCEDURE
A sensitive balance that we can use to measure the force on a short length of current-carrying wire in
a magnetic field. If the balance is so aligned that the end of the U-shaped metal loop is perpendicular
to the field while the sides are parallel to it only the end will be subject to a force from the field. We
can measure the force on the end of the loop by balancing it with a known weight hung from the
other end of the balance.
In this lab, we wish to determine B, the magnetic field of the solenoid; thus we transpose the
equation as follows: B = F/IL. I and L are easily measured, but finding F doesn’t seem quite so
straightforward. However, if we set things up right, we can treat the magnetic force much like a force
produced by some other means. Thus we can measure it by counterbalancing it with a known force.
You can do this by setting up a “see-saw balance,” as described below.
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Insert the blade into the solenoid, with the U-loop Inside as shown. Notice that the blade’s two
rounded clips rest on the L-shaped brackets. These clips act both as pivots and as contact points.
Make sure the clips and the upper surface of the brackets are clean so that good electrical contact
will be made. Balance the blade by adjusting the nut on its outer tip. Then wire the U-loop into the
circuit as shown.
DATA TABLE
OBSERVATIONS
ANALYSIS/CALCULATIONS
CONCLUSIONS
QUESTIONS
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