Linda K
PHYSICS II
LAB #8:
MEASURING RESISTANCE BY A NULL DETECTION METHOD USING A WHEATSTONE BRIDGE
Purpose:
The purpose of this experiment was to measure the resistance at room temperature of a lamp. We also measured the resistance of a cold lamp compared to the resistance of a hot lamp. We also learned the proper techniques of using the Wheatstone bridge.
Materials and Procedure
Wheatstone bridge
Lamp
Alligator Clips
Voltmeter
DC power supply
Galvanometer
10ohm wood
The first step is to wire the apparatus. The lamp is wired to the left side of the wheatstone bridge. One side of the wire is attached on the top of the three metal contacts and the other side is attached to the metal piece running in the center of the top of the wheatstone bridge. A piece of wood with a known resistance of 10ohms is attached to the right, on the top of the three metal contacts. One clip from the voltmeter is attached to the sliding contact, another clip is attached to the piece of metal in the center of the top of the bridge. The power supply is at about 2volts. The sliding contact is then carefully and slowing moved up/down the nicrom wire in order to set the voltmeter to zero finding the balance point (D). One this is found the length on each side if the balance point is measured. The length between the lamp and the sliding contact is L1 and the length between the 10ohm wood and the sliding contact is L2. The power is then disconnected. We move the lamp to the right and the 10ohm wood to the left. We then find the balance point again. L1 is the distance between the lamp and the sliding contact, which is now the length to the right of the sliding contact.
