To determine the resistance of the given wire using a metre bridge and hence to find the resistivity of the material

RESISTIVITY OF THE MATERIAL OF A WIRE

This experiment will determine the unknown resistance of a conductor (wire) by using an instrument known as a meter bridge & to find the resistivity of its material. The meter bridge works on the principle of the Wheatstone bridge. 

Aim of the experiment : 

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

Apparatus required : 

1. Meter bridge
2. Plug Key
3. Resistance box
4. Jockey
5. Galvanometer
6. Connecting wires
7. Battery

Principle of the experiment : 

01. Wheatstone's bridge is balanced when the current through the galvanometer is zero.

02. If P, Q, R & represents the resistances of four arms of Wheatstone's bridge. Then , P/Q = R/S

Formula : 

01. Resistance of the wire (in ohm Ω), R = Sl/(100-l)

Where,

            S - Standard resistance

            l - Balancing length

02. Resistivity of the material of the wire, ρ = πr²R/L

Where,

            R - Resistance of the wire

            L - Length of the experimental wire

            r - Radius of the wire

Circuit Diagram :

Resistance of the given wire using a metre bridge

Procedure : 

• The connections are made as shown in the circuit diagram using connecting wires and the given apparatus.

• Suitable standard resistance S is unplugged into the resistance box.

• Circuit connections are checked for opposite deflections by placing the Jockey at the two ends of the wire from point A to C.

• The Jockey is moved on the wire from end A towards C till the galvanometer shows zero deflection. The balancing length AC = L is measured.

• The resistance of the wire is calculated by using the formula R = Sl/(100-l)

• The experiment is repeated for different values of S and the average value of R is calculated.

• The length " l " and radius " r " of the wire is measured & the values are noted down.

• The resistivity of the material of the wire is calculated by using the formula ρ = πr²R/L

Observation : 

01. Radius of the experimental wire, r = .................. m

02. Length of the experimental wire, L = .................. m

Tabular Column :

Trial No	Resistance, S in (Ω Ohm)	Balencing length, l in (cm)	(100 - l) in (cm)	Resistance, R = Sl/(100 - l) in (Ω Ohm)
01.
02.
03.
04.
05.
				Mean R = ...........Ω

Calculations :

01. Resistance of the wire (in ohm Ω), R = Sl/(100-l) = ..................................Ω
       (Show substitution and calculations for each trial)

02. Resistivity of the material of the wire, ρ = πr²R/L = ..................................Ωm.

Result : 

01. Resistance of the wire, R = ..................................Ω

02. The resistivity of the material of the wire, ρ  = ..................................Ωm.

Note :

01. The value of the balancing length should be between 30cm and 70 cm for accuracy in all Wheatstone's bridge-related experiments.

02. Jockey has to be moved gently over the meter bridge wire.