已知条件是解题的依据,但有些题目中的某些条件并未直接给出,而是隐含在题目之中,解题时应注意挖掘并正确运用,才能使问题迅速获解。 例1 如图1所示,已知R_1=30欧,当滑片P在变阻器的最左端时,伏特表读数为4.5伏,滑片P在变阻器中点时,伏特表读数为3伏。求: Known conditions are the basis for problem solving, but some of the conditions in some topics are not directly given, but are implicit in the topic. Attention should be paid to digging and correct application in order to quickly resolve the problem. Example 1 As shown in Fig. 1, it is known that R_1 = 30 Ω. When the slide P is at the leftmost end of the varistor, the voltmeter reads 4.5 volts, and when the slide P is at the midpoint of the varistor, the voltmeter reads 3 volts. begging: