Resistance

The resistance of a wire is caused by free electrons colliding with the positive ions that make up the structure of the metal. The resistance depends upon several factors:

Length, l Length increases – resistance increases

The longer the piece of wire the more collisions the electrons will have.

Area, A Area increases – resistance decreases

The wider the piece of wire the more gaps there are between the ions.

Temperature Temperature increases – resistance increases

As temperature increases the ions are given more energy and vibrate more, the electrons are more likely to collide with the ions.

Material

The structure of any two metals is similar but not the same, some metal ions are closer together, others have bigger ions.