Measurement of unknown resistance using CareyFoster’s Bridge

06052011, 02:29 PM
Post: #1




Measurement of unknown resistance using CareyFoster’s Bridge
1 Aim of experiment
We are going to determine the value of an unknown resistance using a meterbridge and then make furthur accurate measurements using Carey Foster bridge to take into account the specific resistivity () of the bridge wire. Finally measuring the radius and length of the unknown resistance we can determine the specific resistivity of the material given. 2 Apparatus required a)An unknown resistance b)A known resistance(variable) c)A galvanometer d)A very high resistance of the order of 15000 to protect the galvanometer. e)A dry cell f)A plug key g)A meter bridge with jockey h)A sorting plate i)A copper strip 3 Theory of Experiment Brief discussion and relevant formulae: The Meter Bridge is a device for measurement of resistance using the principle of Wheatstone Network.AB is a uniform wire 100 cm(1m) long, stretched in two segments of 50 cms.AA0,BB0,CC0,DE are thick metal strips which have zero resiatance A0D and BE are gaps in which resistances to be compared are connected. The dry cell is connected through a plug key between A0 and B0. A pivoted galvanometer is connected between the central terminal (F) and sliding contact J through a high resiatance. With a standard resiatance in R the position of jockey is found for which the current in the galvanometer is zero. Then, X R = ResistanceofAJ ResistanceofJB = l 100 − l (1) Using the bridge one can calculate the resistance of the wire from which the specific resistance of the material of wire can be obtained. The CareyFoster Bridge is a modified form of meter bridge. The shorting plate DE is removed so that we get four gaps AD,DC,CE,EB in which resistances can be connected. Two equal resistances P and Q can be connected in gaps DC and CE suppose an unknown resistance and a known resistance are connected in gaps AD and EB. Let the balane point be founf at J(AJ = l) Download full report http://www.cmi.ac.in/~debangshu/lab1/bridge.pdf 

« Next Oldest  Next Newest »
