What influence does the field have on the taconite

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Unformatted text preview: the poles of a magnet are not electric charges? Try it. MEASUREMENT AND ANALYSIS Lay one bar magnet on the Taconite plate. In your journal, draw the pattern of the magnetic field produced. Repeat for each figure in the predictions. CONCLUSION How did your predictions of the shape of the magnetic field for each configuration of magnets compare with your results? What influence does the field have on the Taconite filings? Does the field cause a net force? Does the field cause a net torque? If so, in what direction? 133 PERMANENT MAGNETS – 1302Lab5Prob1 134 PROBLEM #2: CURRENT CARRYING WIRE Your friend's parents, who live on a dairy farm, have high-voltage power lines across their property. They are concerned about the effect the magnetic field from the power lines might have on the health of their dairy cows grazing nearby. They bought a device to measure the magnetic field. The instructions for the device state that it must be oriented perpendicular to the magnetic field. To measure the magnetic field correctly, they need to know its direction at points near a current carrying wire. They know you have taken physics, so they ask you for help. First, you decide to check a simulation of the magnetic field of a current carrying wire. Next, to confirm your prediction and simulation, you decide to use a compass along with a current carrying wire. You decide to investigate both a straight wire and a loop of wire. 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. EQUIPMENT You will have a Hall probe and interface, a magnetic compass, banana cables, a meter stick, an 18volt/5amp power supply and the EMField application. Make sure to use the correct power supply – do not use the Cenco CRT power supplies, they are not designed to be used in this manner! Read the section The Magnetic Field Sensor (Hall Probe) in the Equipment appendix. Read the section Measuring Constant 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. PREDICTIONS Sketch your best guess of the map of the magnetic field near a current carrying wire when the wire is (a) stretched straight, and (b) formed into a loop. EXPLORATION Start the EM Field application. Click anywhere for instructions. 135 CURRENT CARRYING WIRE – 1302Lab5Prob2 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. Choose one by clicking and dragging it into the screen. Under the Field and Potential menu, you should choose the Field Vector option. This option for magnetic fields behaves exactly like that for electric fields. Once you have a clear picture of what the direction of the field is, create a pdf file using the Print command under File. You might also find it useful to play around with different sizes of current to note any changes. Once you are finished with EMField, it is time to move to the physical apparatus. Keep in mind that a compass needle, because it is a small magnet, aligns itself parallel to the local magnet field. Attach enough wires together to give a total length of at least half a meter. Is there any evidence of a magnetic field from a non-current carrying wire? To check this, stretch the wire vertically and move your compass around the center of the wire. Does the compass always point in the same direction? 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 wire to the power supply and turn the power supply on (do not use the Cenco CRT power source). Stretch the wire vertically and move your compass around the wire. Start where you expect the magnetic field to be largest. Is there any evidence of a magnetic field from a current carrying wire? Watch the compass as you turn the current on and off. Does the compass always point in the same direction? How far from the wire can the compass be and still show a deflection? Develop a measurement plan. Now make a single loop in the wire through which you can easily move the compass. Move the compass around the loop. In which direction is the compass pointing? How far away from the loop can you see a deflection? Is this distance larg...
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