Experiment 4 - Magnetic Fields

Experiment 4- - Eric Chong Partner Albert Lee PHYS C1493 Lab Date Experiment 4 Magnetic Fields Introduction In this experiment we observed 2

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Eric Chong PHYS C1493 Partner: Albert Lee Lab Date: October 12, 2006 Experiment 4: Magnetic Fields Introduction In this experiment we observed 2 different ways to measure the magnitude of a magnetic field of an electromagnet induced by a current. The first procedure implemented the idea that the force induced on a current-filled rod of length L will be downwards when placed in a magnetic field (generated by an electromagnet) according to the equation F = iL x B , and by finding the balancing force using weights of mass m and the equation F = mg , we can equate the two functions to find the unknown B . The second procedure, more complex, required a current in a search coil that was induced by a magnetic flux through the coils area A coil , whereby the total charge in the coil is recorded in a charge integrator and the resultant voltage V mag which is proportional to the charge ΔQ by the equation V = K’ΔQ is displayed and recorded. With these values along with the proportionality constant K’ (which is calculated by calibrating the search coil) we can calculate the strength of the magnetic field according to the equation V mag = K’BA coil . Procedure The initial setup of the balance and the current-filled rod needs to be calibrated so that without any magnetic-induced force or weight-induced force, the rod (of length L = 0.105 ± 0.0005 m ) is properly balanced. This is easily done by matching up the balance to a mirror located on the electromagnet fitted with straight lines. Upon doing so, we begin to add washers of mass m = 0.37 ± 0.005 g to the opposite side of the balance from the rod, and alter the current i going through the rod such that the force exerted by the magnetic field equals that of the downward force of gravity – clearly indicated when the balance is parallel to the table (by use of the mirror). This is done for 5 different quantities of equally massed washers, and for 4 different currents of the electromagnet. The current of the electromagnet is set with an uncertainty of ± 0.25 A at levels of 5.0 A, 4.0 A, 3.0 A, and 2.0 A , and the current of the rod is experimentally gauged to an uncertainty of ± 0.005 A. The 2 nd procedure calls for the calibration of the search coil in order to calculate the circuit proportionality constant K’ . We do this by measuring the response V that occurs for a known value of the flux ΔΦ known , experimentally calculated by passing the search coil over the magnetic field of a solenoid B sol induced by a current in the solenoid, I sol , which has n number of turns per meter . The resultant change in flux that is recorded is taken down for different values of
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This note was uploaded on 12/16/2010 for the course PHYS 1493 taught by Professor Lab during the Spring '08 term at Columbia.

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Experiment 4- - Eric Chong Partner Albert Lee PHYS C1493 Lab Date Experiment 4 Magnetic Fields Introduction In this experiment we observed 2

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