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Unformatted text preview: g is a measure of the strength of the monopole. (What are the dimensions of
this “g”?) Determine the direction of the magnetic field from each pole at the point
4. Calculate the magnitude of each component of the magnetic field from each pole at
the point of interest. Add the magnetic field (remember it is a vector) from each
pole at that point to get the magnetic field at that point.
5. Graph your resulting equation for magnetic field strength along that axis as a
function of position along the axis.
6. Repeat the above steps for the other axis. PREDICTION
Calculate the magnetic field strength as a function of distance along each axis of a bar
magnet. Make a graph of this function for each axis. How do you expect these graphs
to compare to similar graphs of the electric field along each axis of an electric dipole? EXPLORATION
Using either a taconite plate or compass, check that the magnetic field of the bar magnet
appears to be a dipole.
Start the MagnetLab program and follow the Hall probe calibration procedure outlined
in the Software appendix. Instructions for using Magnetlab are also displayed in the
Magnetlab Guide Box in the upper right corner of the application.
Take one of the bar magnets and use the probe to check the variation of the magnetic
field. Based on your previous determination of the magnetic field map, be sure to
orient the Hall probe correctly. Where is the field the strongest? The weakest? How far
away from the bar magnet can you still measure the field with the probe?
Write down a measurement plan. 140 MEASURING THE MAGNETIC FIELD OF PERMANENT MAGNETS – 1302Lab5Prob3 MEASUREMENT
Based on your exploration, choose a scale for your graph of magnetic field strength
against position that will include all of the points you will measure.
Choose an axis of the bar magnet and take measurements of the magnetic field strength
in a straight line along the axis of the magnet. Be sure that the field is always
perpendicular to the probe. Make sure a point appears on the graph of magnetic field
strength versus position every time you enter a data point. Use this graph to determine
where you should take your next data point to map out the function in the most
Repeat for each axis of the magnet. ANALYSIS
Compare the graph of your calculated magnetic field to that which you measured for
each axis of symmetry of your bar magnet. Can you fit your prediction equation to
your measurements by adjusting the constants? CONCLUSION
Along which axis of the bar magnet does the magnetic field fall off faster? Did your
measured graph agree with your predicted graph? If not, why? State your results in
the most general terms supported by your analysis.
How would the shape of the graph of magnetic field strength versus distance for the
magnetic dipole compare to the shape of the graph of electric field strength versus
distance for an electric dipole? Is it reasonable to assume that the functional form of the
magnetic field of a monopole is the same as that of an electric charge? Explain your
reasoning. 141 MEASURING THE MAGNETIC FIELD OF PERMANENT MAGNETS – 1302Lab5Prob3 142 PROBLEM #4: THE MAGNETIC FIELD OF ONE COIL
You are working with a group researching new techniques to miniaturize the readwrite head (the device in hard drives that reads and writes data to the disk). You
suggest that a permanent magnet in the head could be replaced with a loop of wire to
control the strength of the magnetic field. You read in your physics text that a coil of
wire carrying a current gives the same magnetic field as a bar magnet: a magnetic
dipole field. Your partners doubt that this is the case, so you decide to check it using a
large coil of wire and a Hall probe, as well as a simulation. You decide to measure the
strength of the magnetic field as a function of position along the central axis of the coil
and compare it to the measurements you have for a bar magnet. As a qualitative check
you also use the Hall probe to make a map of the magnetic field everywhere near the
current carrying coil, and compare that to what the simulation predicts.
Instructions: Before lab, read the laboratory in its entirety as well as the required reading in the
textbook. In your lab notebook, respond to the warm up questions and derive a specific prediction
for the outcome of the lab. During lab, compare your warm up responses and prediction in your
group. Then, work through the exploration, measurement, analysis, and conclusion sections in
sequence, keeping a record of your findings in your lab notebook. It is often useful to use Excel to
perform data analysis, rather than doing it by hand.
Review Measuring the Magnetic Field of Permanent Magnets EQUIPMENT
You have a coil of 200 turns of wire, an 18volt/5amp
power supply, a compass, meterstick, digital multimeter
(DMM), Hall probe and a computer data acquisition
system. You will also have the EMField application. Do
not use the Cenco CRT power supply for this problem. DMM P ower
S upp ly y x Read the sections The Magnetic Field Sensor (Hall Probe) & The Digital Multimeter in the
Read the section Measuring Cons...
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- Spring '14