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lab_34

lab_34 - LAB 34 WHEATSTONE'S BRIDGE and RESISTIVITY...

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LAB # 34: WHEATSTONE'S BRIDGE and RESISTIVITY INTRODUCTION: The Wheatstone bridge (See Fig.1) provides an accurate way of comparing an unknown resistance to a known resistance and thus measuring the unknown. When the bridge has been balanced, i.e., when the current through the galvanometer is zero, the four resistances in the bridge are related by the simple equation (1): 1 2 L L R R s x (1) The Wheatstone bridge will also be used to determine the resistivity of a wire for a given length. Precautions: Keep the power supply voltage at about 1.5 volts in this experiment Prevent excess current through the galvanometer. It is a very sensitive current measuring instrument. To prevent damage, close the shunt (i.e. keep S closed so that much of the Do not push down too hard on the movable contact as to dent the slide wire. Also, do not push down on the wire as you move it. This will ruin its precision since the cross-sectional area along its length will no longer be uniform. APPARATUS: Wheatstone Bridge (slide wire form), Power Supply, banana leads, and 2 DMMs, PC computer with Excel software package. PROCEDURE: Determine the resistivity of the slide wire by measuring the voltage and current of a giving length of wire and using Ohm's Law.

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lab_34 - LAB 34 WHEATSTONE'S BRIDGE and RESISTIVITY...

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