Non-linear V-I graph for filament lamp due to rising resistance

Steps:

• Filament lamps exhibit non-ohmic behavior because resistance increases with temperature.
• Current flow heats the filament, raising its temperature and thus resistance.
• Per Ohm's law (V = IR), with R increasing, V rises non-linearly with I, steepening the graph.
• Select the graph showing a curve that starts relatively flat and becomes steeper.

Why B is correct:

• B shows a curve with increasing slope (dV/dI = R), matching the temperature-dependent resistance increase in filament lamps.

Why the others are wrong:

• A: Straight line indicates constant resistance, typical of ohmic conductors like metals at constant temperature.
• C: Curve bending downward suggests decreasing resistance, opposite to filament heating effect.
• D: Linear but offset or reversed implies fixed or negative resistance change, not applicable.

Final answer: B