To determine the resistivity of two / three wires by plotting a graph for potential difference versus current | CBSE Class 12th Physics Practical

Experiment – 1

Objective:

To determine the resistivity of two wires by plotting a graph for potential difference versus current.

Required Apparatus:

Two resistance wires, a voltmeter (0-3)V and an ammeter (0-3 se) A of appropriate range, a battery/battery eliminator, a rheostat, a meter scale, a one-way key, connecting wires, and a screw gauge.

Formula Used:

By Ohm’s law

Where R is the constant of proportionality, it is known as the resistance of the conductor. R depends on the nature of the material, temperature and dimension of the conductor.

 

Specific resistance (ρ) of the material is given by

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

Circuit Diagram:

Observations:

• Range of ammeter = (0 – 3) A
• The least count of ammeter = 0.05 A
• Range of voltmeter = (0 -3) V
• The least count of voltmeter = 0.05 V
• The least count of metre-scale (L.C.) =0.1 cm

Zero error, e=0 mm,   Zero correction, c = 0 mm

 

For 1st wire:

Length of the given wire, L= 15 cm = 0.15 m

Observation Table for Resistance

Mean value of resistance, R=

.Table for Diameter of wire:

Calculation for Specific Resistance:

Graph – Potential difference versus Current

For 2nd wire:

Length of the given wire, L= 29cm = 0.29cm

Observation table for Resistance:

Table for Diameter of wire:

Calculation for Specific Resistance:

Graph – Potential difference versus Current:

Result:

• Resistance of first wire from table = 1.04 Ω and from graph 1.05 Ω
• Resistivity of 1st wire=48.98×10–⁸ Ω-m
• Percentage error = 0.04%.
• Resistance of 2nd wire from table = 2.06 Ω and from graph = 2.00 Ω
• Resistivity of 2nd wire     =      50.19×10–⁸ Ω-m
• Percentage error = 2.43%.

Precautions:

1. The connection should be neat clean and tight.
2. Thick connections wire should be used for the connections.
3. The voltmeter and ammeter should be of proper range.
4. A low-resistance rehosteat should be used.
5. The key should be inserted only while taking observation to avoid heating of resistance.
6. At one place, the diameter of the wire should be measured in two mutually perpendicular directions.
7. The wire should not make a loop.

Source of Error:

1. The instrument crew may be lose.
2. Thick connection wires may not be available.
3. Rehosteat may have high resistance.
4. The wire may not have uniform thickness.
5. The screw gauge may have faults like a ‘back lash’ error and a wrong pitch.