**Metallic conductors at constant temperature**

The I-V graph of metallic conductor is a straight line pass through the origin. They obey Ohm’s Law, having resistance that is independent of current. (Ohmic conductors)

**Reason:** Resistance in metal is the reduction of the drift velocity of electrons due to collision with the lattice ions. If the temperature of the conductor is kept constant, the magnitude of the vibration of the lattice ions remain the same, and hence it’s resistance would remain the same.

**Filament lamp**

- From the I/V graph, the ratio V/I increases as current increases.
- Resistance of the filament lamp increase with temperature.

**Reason:** As the potential difference across a filament lamp increases, the current increases and the energy dissipated, as heat, increases, resulting in a higher temperature. As the temperature increases, resistance of the filament increases. The collision between the free electrons and the lattice ions increases due to more rigorous vibration of the lattice ions.