Lab 5 - Magnetic Forces 1

Lab 5 - Magnetic Forces 1 - PHY134 Classical Physics II...

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PHY134 - Classical Physics II Laboratory Magnetic Forces - 1 In this experiment we will determine the vertical component of the earth's magnetic field by measuring the deflection of a current-carrying wire stretched between two supports. Equipment Power supply Pulley and table clamp Microscope with calibrated reticule Viewing lamp 50A Current shunt Digital voltmeter DPDT switch Method A thin, flexible copper wire (#31 gauge) is fixed at one end and passed over a pulley at the other. Mechanical tension is maintained by a 20 gram mass, as shown in Figure 1. The power supply enables us to pass an adjustable current I through the wire. A wire segment of length l carrying a current I in the presence of a uniform magnetic field B experiences a force given by: F = I l × B , (1) where l is a vector whose magnitude is the length of the wire segment and whose direction is in the direction of the (conventional) current flow. Q1. Draw a clear, well-labeled diagram showing current flow in the wire, the vector B having the approximate direction of the Earth's field in the laboratory, and the resulting force vector F on the wire
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Viewed from above, the wire will be subjected to a horizontal force distributed along the length of the wire as shown below: Each small wire segment of length d x is subjected to a force d F hor d F hor = I B vert d x , (2) where B vert is the vertical component of the earth's magnetic field in the laboratory. The wire would start moving if its ends were not fixed. Instead, it deflects in approximately the same way that the horizontal cable of a suspension bridge would deflect under a uniform load, as shown in Figure 3. The shape of the wire can be found using the free body diagram of Figure 4. Let the center of the wire be the origin x = 0, y = 0. Let T 0 be the tension in the center of the wire and T ( x ) be the
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