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现行初三教材“研究串联电路”一节,其核心任务是推导出串联电路的总电阻与各串联导体电阻的大小关系。它的推导过程是: 设串联导体的阻值依次为R_1、R_2,串联电路的总电阻为R(图8-27),那么, U=IR,U_1=IR_1,U_2=IR_2 把上列各式代入U=U_1+U_2中,得到 IR=IR_1+IR_2 所以R=R_1+R_2 笔者从教学实践中体验到,上面的推导过程有两点不足:其一,由于学生只知道“导体的电阻”,至于“电路的总电阻”,学生对它还需要有一个感知认识过程,假如就这样将“电路的总电阻”以及“U=IR”直接抛授给学生,学生接受起来很困难;其二,该推导过程得出结论很突然,也显得有
The core task of the current research section “Study Series Circuit” in the third grade textbook is to derive the relationship between the total resistance of the series circuit and the resistance of each series conductor. Its derivation process is: Assuming that the resistance of the series conductor is R_1, R_2, and the total resistance of the series circuit is R (Figure 8-27), then U=IR, U_1=IR_1, U_2=IR_2. Substituting U=U_1+U_2, we get IR=IR_1+IR_2 so R=R_1+R_2 I experienced from teaching practice, the above derivation process has two shortcomings: First, because students only know the “resistance of the conductor”, As for the “total resistance of the circuit”, the student needs to have a process of perceiving and understanding it. If the “circuit’s total resistance” and “U=IR” are simply thrown to the students, students will find it difficult to accept it. Secondly, The derivation process came to a conclusion that it was abrupt and appeared to have