综合实践课上，小薇同学用“伏安法”测量小灯泡的额定电功率，选用的小灯泡上标有“2.5V”字样，已知电源电压恒为4.5V，滑动变阻器的规格为“30Ω 1A”。                                                                                                                                                                                                        

序号	U/V	I/A	P/W
1	1.0	0.18	0.18
2	1.5	0.22	0.33
3	2.0	0.24	0.48
4	2.5