To find the resistance of given wire using a meter bridge and hence determine the specific resistance of the material | Physics Practical Class 12 | Gaurav Kumar

 To find the resistance of given wire using a meter bridge and hence determine the specific resistance of the material.

Aim: -

To find the resistance of given wire using a meter bridge and hence determine the specific resistance of the material.

APPARATUS: -

Meter bridge, galvanometer, Leclanche cell, resistance box,  a wire about 1 m long, connecting wires, meter scale, screw gauge, key, sand paper. 

THEORY: -

OBSERVATIONS: -

1.    Data available for the wire

Material                         =                (usually manganin or constantan)

Gauge (s.w.g.) no.         =                (if Known)

Standard value of specific resistance (form tables)     =    ......................... ohm m

OBSERVATION TABLE FOR RESISTANCE OF WIRE

Observation for Specific Resistance: -

Length of the wire.             =    ............. cm.

Measurement of diameter 

pitch of the screw gauge    =    ............ cm.

No, of divisions on the circular scale     =    100

Least count of screw gauge    =    ............... cm

Zero eroor         =    nil    

    OBSERVATION FOR DIAMETER OF WIRE

Mean corrected diameter          (d) =    .............cm

Mean radius                             (r)    =    ............cm

CALCULATIONS: -

Observation values, L = .............. cm, r = ............... cm and X = ................... ohm

Substitute the values of L, r and X in the working formula, 

and calculate the value of p such that 

                                p = ..................... ohm - cm  = ................. ohm - m 

RESULT: -

Specific resistance of wire is ................ ohm - m.

PRECAUTIONS: -

1.    The connections should be neat, clean and tight. the nends of the connecting wires should be rubbed and cleaned with a sand paper.

2.    The apparatus should be arranged according to the arrangement diagram given in the book and then the connection should be made accordingly.

3.    Plugs in the resistance box should be pressed and made tight by screwing them a little in the clockwise direction.

4.    The key of the battery or the cell should be closed first and then the jockey is touched on wire when the reading is being taken. The jockey key is removed first and then the battery key, immediately after that to minimize the error due to change of resistance by heating.

5.    While moving the jockey to and fro to locate the balance point, the jockey should be lifted again and again and should not be pressed and slided to touch the wore throughout.

6.    While finding out the balance point, the sliding contact should not be pressed too hard, otherwise the uniformity of the wire will be damaged.