Filament lamps exhibit positive temperature coefficient of resistance

Steps:

• Increasing potential difference across the lamp increases current and power dissipation.
• This causes the filament temperature to rise due to heating.
• In metal filaments, higher temperature increases atomic vibrations, impeding electron flow.
• Thus, resistance increases as temperature rises.

Why D is correct:

• Metals like tungsten in filaments follow R = R₀(1 + αΔT), where α > 0, so resistance rises with temperature increase.

Why the others are wrong:

• A: Temperature increases, not decreases, so resistance rises, not falls.
• B: Resistance increases with temperature, not decreases.
• C: Temperature increases, not decreases, though resistance does rise.

Final answer: D