Resistance of a conductor also increases linearly with the temperature. Why and how does this happen?
As temperature increases, the average energy of each particle is higher. Using the analogy of water flow, think of that increase in energy as turbulence in a stream. A stream with lots of energy, like a creek running down a steep hill, has lots of turbulence. Some of the energy of the gravitational potential is used to make the water particles move uphill against the direction of flow. As a result, the total amount of water that moves through the stream may be the same or less than could be moved through a smooth channel with less turbulence and a less steep slope. The resistance of the stream is increased because of the energy that is absorbed by the water molecules moving around chaotically.
Something similar happens in an electrical conductor as the temperature rises. Electrons in a conductor at low temperature move relatively smoothly through the material, while at higher temperatures they are chaotically moving in all directions, including some moving against the direction of the current.