Non-ohmic resistance in filament lamps

Steps:

• Identify that filament lamps have resistance increasing with temperature as the filament heats.
• Apply Ohm's law (I = V/R) where R rises with V, causing non-linear I-V relation.
• Expect a curve starting steep (low R at low V) then flattening (higher R at high V).
• Match to option B, which shows this concave-down shape.

Why B is correct:

• It depicts current rising non-linearly with V, as resistance increases due to thermal effects in the filament, consistent with Ohm's law for variable R.

Why the others are wrong:

• A: Straight line through origin indicates constant resistance (ohmic conductor like a metal wire).
• C: Linear but not through origin suggests constant non-zero resistance, not matching lamp behavior.
• D: Steep initial rise then plateau implies rectification (like a diode), unrelated to lamp heating.

Final answer: B