Resistance

 
3.2  Resistance
 
 
  Ohm's law  
 

Potential difference flowing through a conductor is directly proportional to the electric current when the temperature and other physical properties are kept constant.

\(V = I\times R\)

 
     
 

If Ohm's law is obeyed, the graph against it or otherwise is a straight line as follows:

 
  Ohmic conductor  
 

Conductor which obeys Ohm's Law (Resistance constant)

Example: Constantan wire

 
     
 
  Non-ohmic conductor  
 

Conductor which does not obeys Ohm's Law (Resistance constant)

Example: Filament bulb

 
     
 
 
 
 
 
 
  Resistance of wire  
  \(R=\dfrac{\rho\,l}{A}\)  
     
 

Factors that affect the resistance of a wire

  • Length of wire, \(l\)
    • \(l\) increase, \(R\) increase
  • cross sectional area of wire, \(A\)
    • \(A\) increase, \(R\) decrease
  • resistivity of the wire, \(\rho\)
    • \(\rho\) increase, \(R\) increase
 
 
  Resistivity of a conductor, \(\rho\)  
 
  • a measure of a conductor's ability to oppose the flow of electric current
  • unit is ohm-meter
  • depends on the temperature and the nature of the conductor material
 
     
 
 

 

Resistance

 
3.2  Resistance
 
 
  Ohm's law  
 

Potential difference flowing through a conductor is directly proportional to the electric current when the temperature and other physical properties are kept constant.

\(V = I\times R\)

 
     
 

If Ohm's law is obeyed, the graph against it or otherwise is a straight line as follows:

 
  Ohmic conductor  
 

Conductor which obeys Ohm's Law (Resistance constant)

Example: Constantan wire

 
     
 
  Non-ohmic conductor  
 

Conductor which does not obeys Ohm's Law (Resistance constant)

Example: Filament bulb

 
     
 
 
 
 
 
 
  Resistance of wire  
  \(R=\dfrac{\rho\,l}{A}\)  
     
 

Factors that affect the resistance of a wire

  • Length of wire, \(l\)
    • \(l\) increase, \(R\) increase
  • cross sectional area of wire, \(A\)
    • \(A\) increase, \(R\) decrease
  • resistivity of the wire, \(\rho\)
    • \(\rho\) increase, \(R\) increase
 
 
  Resistivity of a conductor, \(\rho\)  
 
  • a measure of a conductor's ability to oppose the flow of electric current
  • unit is ohm-meter
  • depends on the temperature and the nature of the conductor material