To determine the resistance per unit length of a given wire by plotting a graph for Current (I) versus Potential difference (V)

RESISTANCE PER UNIT LENGTH OF A WIRE

This experiment will determine the resistance per unit length of a given wire by plotting a graph for Current (I) versus Potential difference (V). Resistance is a restriction of the flow of current in an electrical circuit measured in terms of Ohms (Ω).

Aim of the experiment :

To determine the resistance per unit length of a given wire by plotting a graph of Current versus Potential Difference.

Apparatus required :

1. Connecting wire
2. Voltmeter
3. Ammeter
4. Battery
5. Rheostat
6. Plug keys
7. Connecting wires

Principle of the experiment :

Ohm’s Law: " The electric current flowing through a conductor is directly proportional to the potential difference across the ends of the conductor when temperature and physical conditions remain constant "

Hence, Potential difference (V) is proportional to Current (I) or V = RI

Formula :

01. Resistance (in ohm) of the wire R = 1/m

Where, 

            R-Resistance of the given wire.

            m-Slope of the graph of current Vs potential difference.

02. Resistance per unit length (in Ωm^-1) = R/L

Where,

            L-Length of the electrical wire. 

Circuit diagram :

The circuit diagram for the resistance per unit length of a given wire by plotting a graph for Current (I) versus Potential difference (V)

Resistance per unit length of a given wire

Nature of Graph :

Graph for Current (I) Vs Potential difference (V)

Procedure :

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

• A particular value of current (I) is adjusted using a rheostat. The corresponding value of voltage V is noted down.

• The experiment is repeated for different values of I and V & readings are tabulated.

• A graph is plotted between V & I. By considering V on the X-axis and I on Y-axis. The slope "m" of the graph is found.

• Reciprocal of the slope is calculated which gives the resistance R of the wire

• length of the wire is measured.

• The resistance per unit length of the wire is calculated using the given formula.

Observation :

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

Tabular column :

Note down the observed values in the respective tabular column below.

Trial Number	Current I (in Ampere)	Voltage V (in Volts)
1
2
3
4
5
6
7
8
9
10

Calculation :

01. Resistance (in ohm) of the wire R = 1/m = CB/AB = ...................Ω

02. Resistance per unit length (in Ωm^-1) = R/L = ...................Ωm^-1

Result :

Resistance per unit length of given wire is given by = ...................Ωm^-1

Note :

The Plug key (K) should be inserted only while taking the respective observations. In order to avoid the unnecessary heating of the wire.