The circuit shown is used to supply a variable potential difference (pd) to another circuit - AQA - A-Level Physics - Question 28 - 2017 - Paper 1

As the contact C moves from position P to Q, the potential difference across the 10 Ω resistor changes. Initially, at position P, the contact is closer to the higher resistance (5 Ω), thus a larger voltage is across it, while less voltage is across the 10 Ω resistor. As C moves toward Q, more voltage is transferred to the 10 Ω resistor, decreasing the pd across the 5 Ω resistor. Therefore, the graph that correctly represents this is a straight line decreasing from a higher initial voltage to a lower final voltage. The correct option that represents this is: A.