Filament Lamp's Non-Ohmic V-I Curve Due to Heating

Steps:

• Recognize filament lamps as non-ohmic: resistance rises with temperature from current flow.
• Apply Ohm's law (V = IR): as V increases, I rises but R grows, so I increases non-linearly.
• Expect graph starting steep (low R) then flattening (high R) as V rises.
• Select option showing upward curve concave down, matching this behavior.

Why D is correct:

• D shows non-linear curve with decreasing slope, reflecting resistance increase per Ohm's law as filament heats.

Why the others are wrong:

• A: Linear through origin, for constant-resistance ohmic conductors like metals at fixed temperature.
• B: Straight line not through origin, incorrect for any symmetric device starting at zero.
• C: Steep exponential rise, typical of semiconductors like diodes, not gradual heating.

Final answer: D