1. For a metallic conductor, the resistance increases with the increase in temperature. The resistance of filament of bulb is more w hen it is glowing than when it is not glowing. The specific resistance or resistivity also increases with increase in temperature.
2. For alloys (such as constantan and manganin), the resistance and the resistivity remains practically unchanged with the increase in temperature.
3. For semi conductors (such as silicon, germanium, etc.), the resistance decreases with the increase in temperature. eg.: the resistance of carbon also decreases with the increase in its temperature.
