Filament lamp's non-ohmic I-V curve

Steps:

• Recall that a filament lamp has resistance increasing with temperature as current flows.
• Voltage applied causes current to heat the filament, raising resistance and curving the graph.
• Identify the graph showing current rising non-linearly with voltage, steeper at low values then flattening.
• Match this to option A, which depicts the upward-curving line from origin.

Why A is correct:

• Filament lamps follow Ohm's law initially but deviate as resistance rises with temperature, producing a non-linear curve per the I-V relationship for non-ohmic conductors.

Why the others are wrong:

• B shows a straight line, typical for ohmic resistors like wires at constant temperature.
• C shows a diode's exponential curve, allowing current in one direction only.
• D shows a downward curve or no relation, irrelevant to any conductor.

Final answer: A