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Unformatted text preview: tant Magnetic Field in the Software appendix. If equipment is missing or broken, submit a problem report by sending an email to labhelp@physics.umn.edu. Include the room number and brief description of the problem. 143 THE MAGNETIC FIELD OF ONE COIL – 1302Lab5Prob4 WARM UP If you have done the problem Measuring the Magnetic Field of Permanent Magnets, review your lab journal for that problem. If not, answer the warm-up questions below to determine this. 1. Draw a bar magnet as a magnetic dipole consisting of two magnetic monopoles of equal strength but opposite sign, separated by some distance. Label each monopole with its strength and sign. Label the distance. Choose a convenient coordinate system. 2. Select a point along one of the coordinate axes, outside the magnet, at which you will calculate the magnetic field. Determine the position of that point with respect to your coordinate system. Determine the distance of your point to each pole of the magnet, using your coordinate system. 3. Assume that the magnetic field from a magnetic monopole is analogous to the electric field from a point charge, i.e. the magnetic field is proportional to g/r^2 where g is a measure of the strength of the monopole. Determine the direction of the magnetic field from each pole at the point of interest. 4. Calculate the magnitude of the 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 the magnetic field strength along that axis as a function of position along the axis. 6. Repeat the above steps for the other axis. Draw the coil and label the current through it. Using the right hand rule, determine the direction of the magnetic field along the central axis of the coil. Using this information, which symmetry axis of a magnetic dipole corresponds to this central axis? PREDICTION Compare the magnitude of the magnetic field as a function of distance along central axis of a coil of known radius and carrying a known electric current to that of a bar magnet. Also compare the field map of the current carrying coil with that of a bar magnet. 144 THE MAGNETIC FIELD OF ONE COIL – 1302Lab5Prob4 EXPLORATION First, see what the EM Field gives you. Start the application and click anywhere for instructions. To study magnetic fields of current carrying wires, you will want to choose the 2D Line Currents option in the Sources menu. At the bottom of the window, there will be a list of various line currents of different magnitudes. Once you are in the 2D Line Currents mode, you will need to figure out how to model a coil. You should think of the fact that a coil and its field are symmetric about the coil’s central axis and the simulation plots fields in a plane perpendicular to the current flow. Once you have your model of a simple coil input into the program, use the Field Vectors option in the Field and Potential menu to study the field. You should pick points both inside and outside the coil for a complete map of the magnetic field. Once you have done this create a pdf using Print under File. Note: that you will use this for qualitative comparisons only! Now you should start working with the physical apparatus. WARNING: You will be working with equipment that generates 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 a large coil to the power supply. Using your compass, make a qualitative map of the magnetic field produced. To get the most obvious effect on the compass, should the central axis of the coil be oriented N-S or E-W? Using your compass as an indicator, adjust the current up and down to determine the sensitivity of the magnetic field to the current. For a reasonable current in the coil, use the compass to determine how far a measurable magnetic field along the axis of the coil extends. Also check out the magnetic field outside the coil. Is it large or small? Compared to what? Try reversing the current through the coil. What happens to the magnetic field at each point? Connect the Hall probe as explained in the Equipment and Software appendices. Before you push any buttons on the computer, locate the magnetic field strength window. You will notice that even when the probe is held away from obvious sources of magnetic fields, such as your bar magnets, you see a non-zero reading. From its behavior 145 THE MAGNETIC FIELD OF ONE COIL – 1302Lab5Prob4 determine if this is caused by a real magnetic field or is an electronics artifact or both? If you notice an ambient field, can you determine its cause? Go through the Hall probe calibration procedure outlined in the appendix, or in the Magnetlab Guide Box in the upper right corner of the...
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.

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