As voltage increases on a filament and the filament heats, what happens to the current and resistance?

As voltage increases on a filament and the filament heats, what happens to the current and resistance?

• A. Increasing voltage increases current, but resistance increases as temperature rises, giving a curved I–V
• B. Increasing voltage increases current linearly; resistance constant
• C. Current decreases as voltage increases
• D. Both current and resistance decrease

Answer: (A)

The key idea is that a filament’s resistance changes with temperature. When voltage (and thus current) increases, the filament heats up due to power dissipation. For metals, resistance rises as temperature increases because lattice vibrations scatter electrons more, making it harder for current to flow. So as you raise the voltage, the current does go up, but not in a straight-line (ohmic) way—the resistance is changing as the filament heats, producing a curved I–V relationship. The current isn’t constant with voltage, and it doesn’t fall; it increases more slowly because the rising temperature pushes the resistance up.

The key idea is that a filament’s resistance changes with temperature. When voltage (and thus current) increases, the filament heats up due to power dissipation. For metals, resistance rises as temperature increases because lattice vibrations scatter electrons more, making it harder for current to flow. So as you raise the voltage, the current does go up, but not in a straight-line (ohmic) way—the resistance is changing as the filament heats, producing a curved I–V relationship. The current isn’t constant with voltage, and it doesn’t fall; it increases more slowly because the rising temperature pushes the resistance up.