EM6_Manual

EM6_Manual - General Physics II Lab EM6 The Current balance...

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General Physics II Lab EM6 The Current balance General Physics II Lab EM6 The Current Balance Purpose In this experiment, you will learn the basic operation of the current balance and use it to measure the magnetic force on a current-carrying wire. Equipment and components Electronic balance, dual channel power supply, multimeter ( × 2), switch box, transparent shielding box, electromagnet with coil and core, lab jack, conducting wire segment ( × 4), and calipers. Background A current-carrying wire in a magnetic field experiences a force that is usually referred to as a magnetic force. The magnitude of this force depends on four variables: the current I , the length of the wire L , the strength of the magnetic field B , and the angle θ between the magnetic field and the wire. The mathematical expression for the magnitude of this force is given by F = ILB sin θ . (1) The vector form of the magnetic force is given by a vector cross product: F = I L × B , (2) where the vector L is directed along the length of the wire. In a differential form, Eq. (2) can be written as dF = I dl × B , (3) where the vector dl is directed along the length of the wire segment dl . Procedure I. Experimental setup and calibration Figure 1 Experimental setup Revised: 22 July 2009 1/10
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General Physics II Lab EM6 The Current balance Figure 1 shows the experimental setup. The coil of the electromagnet is connected in series with an output of the dual channel power supply via a multimeter (which serves as an ammeter) and a polarity switch. The conducting wire segment is connected via two flexible copper wires and a multimeter (which serves as an ammeter) to another output of the power supply to form a conductor loop. The two flexible copper wires should be kept slightly loose, so that they do not exert any force on the conducting wire segment. Figure 2 below shows a close-up of the current balance. Figure 2 Close-up of the current balance Caution: The electromagnet coil will become hot during the experiment. Beware of handling it. Never set the current of the circuit above the maximum current limit allowed, which is 1.0 A for both the electromagnet coil and the wire segment. The flexible copper wires attached to the wire segment are very fragile, please handle them carefully. 1. Fix the coil and core on the lab jack and connect the electromagnet circuit, as shown in Fig. 1. Record the length L g of the air gap of the electromagnet in the lab report. 2. Remove any loading on the pan of the electronic balance and then turn on the balance.
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EM6_Manual - General Physics II Lab EM6 The Current balance...

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