What NORMALLY causes the resistance of a conductor to increase?

The increased resistance of a conductor is primarily attributed to an increase in temperature. As temperature rises, the atoms within the conductor vibrate more vigorously. This heightened activity causes more collisions between the conduction electrons and the vibrating atoms, leading to a disruption in the flow of electrons. As a consequence, the overall resistance experienced by the conductor becomes greater.

In contrast, increasing the size or diameter of a conductor generally leads to a decrease in resistance, as there is more space for electrons to flow through. Similarly, decreasing the length of the conductor also contributes to reduced resistance, because electrons have a shorter distance to travel before reaching their destination. On the other hand, decreasing the temperature often results in lower resistance, as the atomic vibrations diminish, allowing electrons to flow more freely. Therefore, the primary factor that causes resistance to increase is an elevation in temperature.