Series circuit: resistance from V-I graph at given current

Steps:

• Components in series share the same current of 0.3 A.
• From the V-I graph, read the voltage across the filament lamp at I = 0.3 A.
• Calculate lamp resistance using R = V / I.
• Divide the graph's voltage value by 0.3 A to get 12 Ω.

Why B is correct:

• At 0.3 A, the lamp's V-I graph shows V = 3.6 V; R = 3.6 V / 0.3 A = 12 Ω, matching Ohm's law for the operating point.

Why the others are wrong:

• A: 0.6 Ω implies V = 0.18 V, too low for typical lamp curve at 0.3 A.
• C: 15 Ω implies V = 4.5 V, overestimating the non-linear lamp voltage.
• D: 18 Ω implies V = 5.4 V, exceeding the graph's value for the lamp.

Final answer: B