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Unformatted text preview: Michael Lin Tuesday Section Partners: Josh Narciso, Bryant Rolfe Due Date: 2/27/07 Magnetic Fields Michael Lin The objective was to determine the strength of the magnetic field in the gap of an electromagnet by two methods: measuring the force on a current-carrying rod, and by observing the change in magnetic flux by removing a search coil from a region containing the magnetic field. The magnetic fields measured by these two methods for different current values were significantly different, and it cannot be determined which of the two is more accurate. However, in terms of precision, the measurement via a current carrying rod is more precise than the measurement through change in flux, as the uncertainties in the measurements are smaller. INTRODUCTION The first method to measure the magnetic field in a region of space is to measure the amount of force that a current carrying conductor such as a wire or rod feels in the presence of a magnetic field. For a wire or rod of length L carrying a current I, the deflecting force experienced by this conductor will be proportional to B, where L is a vector representing direction of current flow and B is a vector representing direction of the field. F = iL x B If the current I, the length L, and the deflecting force F can be measured, then it is possible to calculate and predict the strength of the magnetic field B. The second method to measure the magnetic field in a region of space is to observe the change in flux by removing a closed conducting loop (search coil) from the magnetic field. The flux of field lines through a closed conducting loop of area A that is placed in a region with a magnetic field B is given by the equation: Φ=∫B•ndA If the plane of the loop and the direction of the magnetic field lines are perpendicular, then the flux through the loop is reduced to the equation Φ=BA. Faraday’s law explains that as flux changes with time, then an EMF (or voltage) will be induced across the conducting loop. The current that is driven through the loop by this EMF can be measured, and then the voltage can be extracted. Once the voltage is known, it can be used to calculate the strength of the magnetic field B. EXPERIMENTAL Materials and Methods The equipment used in this experiment to measure magnetic field strength were the electromagnetic, voltage (power) supply, current balance, search coil, solenoid, integrator circuit, and voltmeter. Experimental Method For the first part of the experiment, after initial measurements had been taken and the equipment set up (initial calibration ensuring a level balance before the addition of any masses), different masses of weights were placed on the balance, and the balance current was adjusted so that the balance was level. The masses and currents were recorded for many trials, with the current in the electromagnet level....
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This note was uploaded on 03/05/2008 for the course PHYS 1494 taught by Professor Carlo during the Spring '08 term at Columbia.
- Spring '08