The calculation of very small resistances using Wheatstone bridge The change of the resistance with wire radius and wire typeResistance table, DC power supply, resistor set (0.4 ve 47ohm), multimeter, connection cables, wires: 0.2, 0.4, 0.6 mm Cr-Ni, 0.6 mm brass, 0.6 mm bronze.
Technical InformationThe known resistance in the Wheatsone bridge is R, and the resistance to be measured is a thin wire. The wheatstoen table includes 5 wires connected. These are Cr-Ni wires of 0.2,0.4,0.6 mm radii and brass and bronze wires of 0.6 mm radius. In addition another Cr-Ni wire of 0.4 mm and 1 m of length is used as reaosta since it has a movable head. If the distances on the left and right of this head are L1, L2 these correspond to the resistances R1 and R2 since resistance is linearly dependent on the wire length. These lengths can easily be measured from the ruler on the table. The resistance of a wire is given by the equation: R=rL/A where r is the resistivity, L is the length and A is cross section area of the wire. The Wheatstone connection is made such that four resistances are known R, Rx to be measured (one of the wires) and R1 and R2 are the left and right side reosta wires. After connection is done, the reosta head is moved until the multimeter connected to the middle of R-Rx and R1-R2 reads zero current. At this adjustment, the lengths are measured and the resistance to be measured is calculated from Rx=RL1/L2.
