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电路分析中涉及较多的物理量,有时会出现未知量的个数多于方程的个数的情形。在数学上该类方程属于不定方程,即具有不确定解。但是,在物理问题的定量分析中,洞察方程的结构及设问要求,有时可以通过等效变换,使不定方程转化为定方程,其解具有惟一性。另外,电路中常常出现电阻变化的情形,而电阻的变化又会引起电路中电压、电流的变化,推理中要理解表达式R=(ΔU)/(ΔI)的成立条件。
Circuit analysis involves more physical quantities, and sometimes there will be more unknowns than the number of equations. Mathematically such equations are indeterminate equations, that is, with indefinite solution. However, in the quantitative analysis of physical problems, it is necessary to understand the structure of the equation and ask for questions. Sometimes it is possible to transform the indefinite equation into a fixed equation through the equivalent transformation, and the solution is unique. In addition, the circuit often appear resistance change situation, and resistance changes will cause the circuit voltage and current changes, reasoning to understand the expression R = (ΔU) / (ΔI) the establishment of conditions.