How to find the resistance of given wire using meter bridge ….

Experiment : To find the resistance of given wire using meter bridge and hence determine the specific resistance (resistivity) of its material .

Apparatus : A meter bridge (slide wire bridge) , a Leclanche cell (battery eliminator ) , a galvanometer , a resistance box , a jockey , a one way key , a resistance wire , thick connecting wires , a screw gauge , a meter scale , a set square and sand paper .

Theory :

(i) Unknown resistance X is given by

$\displaystyle X = \frac{(100-l)}{l} R $

where R is known resistance placed in the left gap and unknown resistance X in the right gap of meter bridge . l is the length of meter bridge in cm from zero end up to the balance point .

(ii) Specific resistance ρ of the material of the given wire is given by

$\displaystyle \rho = \frac{X \pi D^2}{4 L} $

Where L is the length and D is the diameter of the given wire .

Procedure :

For Resistance

(i) Arrange the apparatus in the proper manner .

(ii) Find the least count of the screw gauge . With the help of screw gauge measure the diameter of the wire of which resistance is to be determined .

(iii) Clean the insulation at the ends of connecting wires with a piece of sand paper . Tighten all plugs of the resistance box gently pressing each plug .

(iv) Connect the resistance wire whose resistance is to be determined in the right gap

(v) Connect resistance box of low range in the left gap .

(vi) Take out some resistance from the resistance box and plug the key (K)

(vii) Touch the jockey gently first at left end and then at right end of the bridge wire .

(viii) Note the deflection in galvanometer .If the galvanometer shows deflection in opposite direction then connection are correct .If the deflection is only one sided then there is some fault in the circuit . Check the circuit again especially of the junctions .

(ix) Move the jockey gently along the wire from left to right till galvanometer gives no deflection .

(x) Repeat the above steps for at least four times with different with different values of R .

(xi) Record your observations .

For Specific Resistance

(xii) Cut the resistance wire at the points where it leaves the terminals , stretch it find its length with the help of metre scale .

(xiii) Measure the diameter of the wire at least at four places in two mutually perpendicular directions at each place with the help of screw gauge .

(xiv) Record your observations