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Unformatted text preview: the magnetic field strength
versus position along the axis. EXPLORATION
WARNING: You will be working with a power supply that can generate large
electric voltages. Improper use can cause painful burns. To avoid danger, the power
should be turned OFF and you should WAIT at least one minute before any wires
are disconnected from or connected to the power supply. NEVER GRASP A WIRE
BY ITS METAL ENDS!
Connect the large coils to the power supply with the current flowing in opposite directions
in the two coils, using the adjustable voltage. With the compass, explore the magnetic
field produced. Be sure to look both between the coils and outside the coils.
Now connect the large coils to the power supply with the current flowing in the same
direction in each coil, using the adjustable voltage. With the compass, explore the
magnetic field produced. Be sure to look both between the coils and outside the coils. 154 MEASURING THE MAGNETIC FIELD OF TWO PARALLEL COILS – 1302Lab5Prob6
Based on your observations, should the currents be in the same direction or in opposite
directions to give the most uniform magnetic field between the coils?
Connect the Hall probe according to the directions in appendices. For the current
configuration that gives the most uniform magnetic field between the coils, explore the
strength of the magnetic field along the axis between the coils. Follow the axis through
the coils. Is the field stronger between or outside the coils? Where is the field strongest
between the coils? The weakest?
See how the field varies when you are between the two coils but move off the axis. How
far from the axis of the coils can you measure the field? Is it the same on both sides of
the coils? Decide whether to set the amplifier to high or low sensitivity.
When using the MagnetLab program, consider where the zero position should be to
simplify comparison with your prediction.
Write down a measurement plan. 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.
Use the Hall probe to measure the magnitude of the magnetic field along the axis of the
coils of wire. Be sure to measure the field on both sides of the coils.
What are the units of your measured magnetic fields? How do these compare to the
units of your prediction equations?
Use the DMM to measure the current in the two coils. As a check, repeat these
measurements with the other current configuration. ANALYSIS
Graph the measured magnetic field of the coil along its axis as a function of position
and compare to your prediction. CONCLUSION
For two large, parallel coils, how does the magnetic field on the axis vary with distance
along the axis? Did your measurements agree with your predictions? If not, explain.
Describe the limitations on the accuracy of your measurements and analysis. 155 MEASURING THE MAGNETIC FIELD OF TWO PARALLEL COILS – 1302Lab5Prob6 Does this two-coil configuration meet the requirement of giving a fairly uniform field?
Over how large a region is the field constant to within 20%? This very useful
configuration of two coils (distance between coils equals radius) is called a Helmholtz
coil. 156 PROBLEM #7: MAGNETS AND MOVING CHARGE
You are leading a technical team at a company that is redesigning the cathode ray tubes
(CRT’s) used for computer monitors. To introduce this project to a group of
stockholders, you need to demonstrate how an electron beam can be moved across a
screen by a magnetic field. You decide to use an ordinary bar magnet held outside of
the CRT to deflect the electrons. Before you do the demonstration, you need to know
the qualitative effect of bringing a bar magnet up to a CRT. In the laboratory you
qualitatively determine how the direction and size of the electron deflection is related to
the magnetic field direction, the magnetic field strength, and the velocity of the electron.
You also determine how the deflection is affected by how close the magnet is held to the
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 Deflection of an Electron Beam by an Electric Field EQUIPMENT
You have a cathode ray tube (CRT), banana cables, Cenco CRT power supply, bar
magnet, a meterstick, and a compass.
Read the sections Cathode Ray Tube (CRT) and Accessories and Magnetizing a Bar Magnet
in the Equipment appendix.
If equipment is missing or broken, submit a problem report by sending an email to
[email protected] Include the room number and brief description of the
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.
- Spring '14