Resistance and Resistivity
The resistance of an electrical conductor depends on four factors, these being: (a) the length of the conductor, (b) the cross-sectional area of the conductor, (c) the type of material and (d) the temperature of the material.
Resistance, R, is directly proportional to length, l, of a conductor. For example, if the length of a piece of wire is doubled, then the resistance is doubled.
Resistance, R, is inversely proportional to cross-sectional area, a, of a conductor, i.e., R is proportional to 1/a. Thus, for example, if the cross-sectional area of a piece of wire is doubled, then the resistance is halved.
Since R is proportional to l and R is proportional to 1/a, then ...