what factors do the sensitiveness & accuracy of a carey foster's bridge depend?

Answer 1

Sensitivity of Carey foster bridge is the same as the sensitivity of the Wheatstone bridge as it uses the same fundamental principle. The bridge is balanced when the two pairs of resistances connected to the galvanometer bear the same ratio. This can happen even when all the four Resistances are not of the same order. It can be proved that the bridge is most sensitive when all the four Resistances are of the same order. In a meter bridge the Resistances of the two parts of the wire are of the same order as the unknown and known resistances are of the same order. for a given meter bridge this is not always possible for any arbitrary resistance. For example if I have to find the value of some unknown resistance of about 100 ohms with a metre bridge wire of say 4 ohms Resistance. Then the bridge will not be so sensitive. In Carey foster bridge this problem is over come by taking two standard resistances of the same order in addition so that they in series with the wire make the new ratio arms; similar arguments can be made for resistances of the order of fraction of ohms.The other advantage of the Carey foster bridge is that it eliminates the end resistances. As far as accuracy is concerned that would also depend upon the sensitivity of the galvanometer or detector.