Filament Lamp Behavior with Increasing Current

Steps:

• Current through the filament causes heating via Joule's law (P = I²R).
• Increased current raises power dissipation, elevating filament temperature.
• Higher temperature increases resistance in the metal filament.
• This results in brighter light emission from the hotter filament.

Why D is correct:

• Joule's heating law states power increases with I², directly raising filament temperature as current grows.

Why the others are wrong:

• A: Brightness increases due to higher temperature and light output.
• B: Resistance increases with temperature in metals, per positive temperature coefficient.
• C: Potential difference (V = IR) typically increases as both I and R rise.

Final answer: D