A lamp and a resistor R=10Ω are connected in series to a variable DC supply. The current I through the circuit is measured for different supply voltages Vs. The following data are obtained:
(i) Using the readings in the table, calculate the potential difference VR across the resistor for each supply voltage.
Vs (V): 3, 6, 9, 12
I (A): 0.20, 0.35, 0.45, 0.50
(ii) Hence determine the potential difference Vlamp across the lamp for each case.
(iii) Plot (qualitatively) the Vlamp–I graph for the lamp and state whether the lamp obeys Ohm’s law, giving a reason.
(iv) Discuss how the presence of the ohmic resistor in series influences the overall shape of the circuit’s V–I characteristic at low and at high supply voltages.