To find resistance of a given wire using a metre bridge and hence determine the resistivity (specific resistance) of its material.

Aim - To find resistance of a given wire using a metre bridge and hence determine the resistivity (specific resistance) of its material.

Materials Required - A metre bridge, Battery Eliminator, Galvanometer, Jockey, Rheostat, Connecting Wires, An Unknown constantan wire, A metre scale.

Theory - We know that a metre bridge works on the principle of a balanced Wheatstone bridge and the value of an unknown resistance can be easily calculated by the given formula.

=> The unknown resistance X is given by,

X = ( 100 - L ) / ( L x R )

where R is known resistance places in the left gap and unknown resistance X in the right gap of metre bridge. 'L' cm is the length of the metre bridge wire from zero end up to balance point.

=> Specific resistance (ρ) of the material of the given wire is given by.

ρ = R x A / L

ρ = ( R x π x D²/ 4 x L )

=> where, L is the length and D is the diameter of given wire.

Procedure - Draw the proper circuit diagram, arrange the apapratus accordingly with tight connections. Check the right and left end deflections on Galvanometer by touching the jockey to the knobs and then turn by turn find null points with different amount of resistances and note the lengths. Put the values in formula to find the unknown resistances as well as resistivity.

Circuit Diagram - The labelled circuit diagram for the given experiment "To find resistance of a given wire using a metre bridge and hence determine the resistivity (specific resistance) of its material. " is shown below. The diagram is to be made on the left blank side of the practical book

Observations -

Resistances considered : 1 , 2 , 3 , 4 , 5 ohms

Null points : 42.9 , 56.4 , 65.6 , 76.2 , 82.5 centimeters

Number of readings taken : 3

Observation Table -Take your observations properly and record them in the following table.

TABLE 1 : To determine, find and calculate unknown Resistance from meter bridge .

Sr No.	Resistance (R) from the known Resistance box [in Ohms - Ω]	Length (L) AB on meter scale [in cms]	Length (100-L) BC on meter scale [in cms]	Unknown Resistance (X) X=R(100-L) / (L) [in ohms - Ω]
1	1 Ω	42.90 cm	57.10 cm	1.33 Ω
2	2 Ω	56.46 cm	43.50 cm	1.54 Ω
3	3 Ω	65.53 cm	34.46 cm	1.57 Ω
4	4 Ω	76.26 cm	23.73 cm	1.24 Ω
5	5 Ω	82.53 cm	17.46 cm	1.05 Ω

Results - The resistance of the unknown resistor X is approximately 1.4 ohm and it coincides with the theoretical value and confirms our experiment verification.

Precautions - The connections should be neat, clean , tight.

- All the plugs in the resistance box should be tight.

- Move the jockey gently over the bridge wire, don't rub it .

- The plug in key should be inserted properly for observations.

- Use set squares to avoid errors due to parallax.

- The wire should not make a loop.

- Note readings quickly because the wire gets heated quickly and shows different readings.

Sources of Error - The instrument screws may be loose.

- The plugs may not be clean.

- The wire may not have uniform thickness.

- The arrangement might not be stable.

________________________________________________________________________________________________________

View the Practical As Handwritten PDF File

If you experience any problem viewing or exploring the pdf or the blog post please instantly contact us at the contact form or you can message any of our official handles. Mistake pointing would be whole heartly accepted .

Link to download the pdf file - ( Link for PHYSICS CLASS 12 PRACTICAL - 2 )

_______________________________________________________________________________________________________

Viva Questions Relevant to the Practical

Q1 What is meant by resistance of a wire in a circuit ?

Ans . When the charge particles move across the wire there are particles of the wire or positive charge particles which act as obstacles in their path and cause an opposition to the flow of current. This ability to resist the flow of current by the wire is termed as Resistance . Its SI units are Ohms .

Q2 Which wire is best to use as connecting wire in home appliances ?

Ans . Copper wire is the best choice for connecting wires in home appliances due to its high electrical conductivity, low resistance, durability and copper is readily available and cost-effective. The high electrical conductivity, durability, and affordability of copper make it the best choice for connecting wires in home appliances. Its use ensures optimal electrical performance and long-term reliability

Q3 Why did we connect the voltmeter as parallel combination to the wire ?

Ans . In parallel combination since the starting and ending points are all connected together at both ends, so there is no voltage difference between all the circuit elements connected to that points and hence because voltage is same for all , so the amount of current flowing to the resistance wire would not be altered due to the involvement of the Voltmeter. The voltmeter was connected in parallel to measure the wire's potential difference accurately without altering the current. Parallel connection ensures minimal disturbance to the circuit and allows direct voltage measurement across the wire.

_________________________________________________________________________________________________