Non-linear I-V curve from temperature rise in filament

Steps:

• Identify ohmic components (B, C) produce straight lines through origin due to constant resistance.
• Note diode (D) shows current in forward bias only, zero in reverse.
• Recognize filament lamp (A) starts linear but curves upward as filament heats, increasing resistance.
• Match curve to filament lamp's characteristic.

Why A is correct:

• Filament lamp follows Ohm's law initially but resistance rises with temperature (R = ρL/A, ρ increases), yielding non-linear I-V graph.

Why the others are wrong:

• B: Metallic conductor at constant temperature has fixed resistance, producing linear I-V graph.
• C: Fixed resistor obeys Ohm's law strictly (V = IR), giving straight-line graph.
• D: Semiconductor diode conducts unidirectionally, with I-V graph showing forward current and reverse blocking.

Final answer: A