Range of resistivities

Current (I) is the rate of flow of charged particles and so can be calculated by considering the following factors:

• The number of charged particles travelling across a conductor- 
• The charge carrier density (n) of a material describes the number of charge carriers it contains per unit volume.
• The speed at which the charged particles are travelling  
  • Charged particles in a conductor are constantly colliding with other particles in the conductor and so do not travel straight through a conductor, so the average speed at which they move along the conductor must be considered. This is called the drift velocity (v).
• The charge (q) that a single charged particle carries -
• This value is 1.6 × 10^-19 C for electrons.

Therefore, the current passing through a conductor can be calculated by using the formula below:

I = nqvA

Where n is the charge carrier density, q is the charge of a charge carrier, v is the drift velocity and A is the cross-sectional area of the object.

Different materials have different values of charge carrier density , and even the same material has different values for different temperatures. This is because, when a material is given more energy (in the form of heat), some of its atoms may release more charge carriers, increasing the charge carrier density. This is why there is a large range of resistivities of different materials.