Factors Affecting Resistance and How They Affect

Factors Affecting Resistance & How They Affect

Resistance is:

  • Directly proportional to the length of the conductor.
  • Directly proportional to the nature of the conductor.
  • Directly proportional to the temperature of the conductor.
  • Inversely proportional to the cross-sectional area of the conductor.

1.  Length of a Conductor: Consider a Copper wire of length 1 m and connect it between terminals A and B of the circuit. Note the reading of the ammeter. Now take another copper wire of the same area of cross-section but of length 2 m. Connect it between terminals A and B by disconnecting the previous wire. Again, note the reading of the ammeter. It will be found that the reading of the ammeter (i.e., electric current) in the second case is half of the reading of the ammeter in the first case. 

  • Since I = V / R so the resistance of the second wire is double the resistance of the first wire. 
  • It shows that the resistance of a conductor is directly proportional to the length of the conductor. 
  • Thus, more is the length of a conductor, more is its resistance. 

2.  Area of the cross-section of a Conductor: Now take two copper wires of the same length but of a different area of cross-sections. Let the area of the cross-section of the first wire is more than the area of the cross-section of the second wire. Connect the first wire between terminals A and B in the circuit shown in the figure above. Note the reading of the ammeter. Now disconnect the first wire and connect the second wire between terminals A and B. Again note the reading of the ammeter. It will be found that the reading of the ammeter (i.e., electric current) is more when the first wire (i.e., thick wire) is connected between A and B than the reading of the ammeter when the second wire (i.e., thin wire) is connected between the terminals A and B. 

  • It shows that the resistance of a conductor is inversely proportional to the area of cross-section of the conductor. 
  • Thus, the resistance of a thin wire is more than the resistance of a thick wire.

3.  Effect of the Nature of material: Take two identical wires, one of copper and the other of Aluminium. Connect the copper wire between terminals A and B. Note the reading of the ammeter. Now, connect the aluminium wire between terminals A and B. Again note the reading of the ammeter. It is found that the reading of the ammeter when the copper wire is connected in the circuit is more than the reading of the ammeter when the aluminium wire is connected in the circuit. 

  • This implies that the resistance of the copper wire is less than the resistance of the aluminium wire. 
  • Hence, the resistance of a wire or a conductor depends upon the nature of the material of the conductor.

4.  Effect of temperature of the conductor: If the temperature of the conductor connected in the circuit increases, its resistance increases.