Remember to calibrate the hall probe before you turn

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Unformatted text preview: h the magnetic field and the color seen by the eye. Is the change in color gradual with a slow change in the angle? Is the relationship between color change and angle change linear (i.e. does the same amount of angle change always seem to cause the same amount of color change?) Does the eye in the simulation “see” what you expected it to? Why or why not? Now examine the apparatus with which you will make your measurement. Remember to calibrate the Hall probe before you turn on the coils. You will want as large a magnetic field as you can produce safely with the equipment available. Check to see if the magnetic field varies in time. Move the sensor slightly without changing its orientation to see if the magnetic field changes with position in the region of the sensor. If it does, this will add to the uncertainty of your measurement. Slowly rotate the Hall Probe sensor through a complete circle noting the size of the readings. What is the best way to read the angle? When you return to the same angle, do you get the same reading? For what orientation(s) is the magnetic flux largest? Smallest? Is that as you expected? Make sure you understand the correspondence between the simulation program, the measurement apparatus, and the objects in the problem statement. MEASUREMENT Use the Hall probe to measure, for a particular angle, the magnitude of the magnetic field between the Helmholtz coils. Rotate the probe through 360 degrees, making measurements at appropriate angle intervals. Record uncertainties with the data. ANALYSIS Describe the color and intensity change seen by the eye as the frame rotates. What does this represent? 175 MAGNETIC FLUX – 1302Lab6Prob2 After the Hall probe measurement, choose an equation, based on your prediction, that best represents your data points and adjust the coefficients to get the best correspondence with the data. CONCLUSION How is the magnetic flux through the coil dependent on the angle it makes with the magnetic field? Is the flux ever zero? When is the flux a maximum? How did the results compare to your prediction? 176 PROBLEM #3: THE SIGN OF THE INDUCED POTENTIAL DIFFERENCE For the next polar expedition, your engineering firm has developed an electric generator that can operate in extreme conditions. The expedition team is convinced that they need to understand generators, “just in case one breaks.” You find yourself trying to describe to the leader how the sign of the induced potential difference across the ends of a coil of wire depends on the physical arrangement and relative motions of the materials. You decide to do a quick demonstration with the simplest situation possible; you first push the north pole of a bar magnet through the coil, and then you repeat with the south pole of the magnet. What happens? What else could you do with the same equipment? 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. Read: Tipler & Mosca Chapter 28.2. EQUIPMENT You have a small coil of wire and a bar magnet. You will use the voltage probe with the VoltageTimeLAB software. S N A mmet er Read the section Magnetizing a Bar Magnet in the Equipment appendix if you need to remagnetize your magnets. Read the section VoltageTimeLAB - MEASURING TIME-VARYING VOLTAGES 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. 177 THE SIGN OF THE INDUCED POTENTIAL DIFFERENCE – 1302Lab6Prob3 WARM UP 1. Draw a picture of each situation. Draw and label the velocity vector of the magnet relative to the coil. Also draw the direction of the magnetic field vectors in the coil. 2. Use Lenz’s Law to relate the changing flux through the coil to the sign of the potential difference induced across the ends of the coil? How does the induced potential difference across the ends of the coil relate to the induced current in the coil? PREDICTION Restate the problem. How do you determine the sign of the induced potential difference across the ends of a coil of wire? EXPLORATION Plug the voltage probe into the SensorDAQ interface using the required Ch. 1. Attach the clips to the two ends of the coil and start the VoltageTimeLab program. Make sure you read the software appendix if necessary. Using the magnet and the coil, make sure that the apparatus is working properly and that you are getting appropriate potential difference graphs on the screen. Push one end of the magnet into the coil and note the sign of the induced potential difference. Is t...
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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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