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INDIANA UNIVERSITY, DEPARTMENT OF PHYSICS, P309 LABORATORY Laboratory #1: Electrical Measurements I Goal: Learn to measure electrical quantities; investigate the properties of electrical meters, batteries and power supplies. Equipment: Batteries (dry cells), digital multi-meters (DMM), assorted resistors and variable resistor bank, regulated DC power supplies. (A) Battery: example of a real voltage source A battery is a voltage source, or a device that produces a voltage difference V S between its poles. Let us connect a &load± resistor R L between these poles. The smaller the resistor, the more current flows. As we lower this resistor, eventually the chemical reaction inside the battery cannot keep up with the demand and the voltage V across the battery drops, or V < V S . This behavior is as if there is an &output± resistance R S inside the battery that limits the current flow. Such a &real± battery is shown in fig.1. In order to measure R S , connect a variable load (resistor bank) and a voltmeter across the battery as shown in fig.2. In addition, insert a second DMM as a current meter in the circuit to measure the current I through the load resistor. Start at a large load (k ) and work your way down until I has become a few mA. Continue till you draw about 100 mA. Be aware that a small R L means a large current, which alters the battery irreversibly. Be reluctant to apply small loads and if you do, only for the duration of the reading. fig.2
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This note was uploaded on 01/20/2012 for the course P 309 taught by Professor Urheim during the Spring '11 term at Indiana.

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