帮我讲解这道题---**Extraction Content:** **Question Stem:** 例题 在图甲电路中，电源电压恒定，R1为滑动变阻器，R2为定值电阻。开关S闭合后，将滑动变阻器的滑片从一端移至另一端的过程中，变阻器的电功率P随其阻值R1的变化关系如图乙所示。下列对电路的表述中，都正确的是 ( ) **Numbered Statements:** ①电源电压为6V ②R2的阻值为1Ω ③电流表示数的变化范围为0.75A~1.5A ④R1的最大功率为2.25W **Options:** A ①② B ②③ C ①③ D ①④ **Circuit Diagram Description (图甲):** * Type: Electrical circuit diagram. * Components: * A power source (symbol shows positive and negative terminals). * A switch (S). * A variable resistor (R1) with an arrow indicating the slider position. A voltmeter (V) is connected in parallel across R1. * A fixed resistor (R2). * An ammeter (A) connected in series with R1 and R2. * Connections: The power source, switch S, ammeter A, variable resistor R1, and fixed resistor R2 are all connected in series, forming a closed loop. The voltmeter V is connected in parallel across R1. **Graph Description (图乙):** * Type: 2D Line chart (a curve). * Axes: * X-axis: Labeled "R1/Ω", representing the resistance of R1 in Ohms. Scale is marked at 0, 2, 8, and extends beyond 8. * Y-axis: Labeled "P/W", representing the power dissipated by R1 in Watts. Scale is marked at 0 and 2, and extends beyond 2. * Curve: The curve shows the relationship between P and R1. It starts from (0, 0), increases to a peak, and then decreases. * Data Points/Features: * The curve passes through the origin (0, 0). * At R1 = 2 Ω, P = 2 W. * At R1 = 8 Ω, P = 2 W. * The curve reaches a maximum value somewhere between R1=2 and R1=8. The peak power is indicated by the dotted line extending from the maximum point to the Y-axis. **Other Relevant Text:** None beyond the question, statements, options, and diagram/graph labels.