先看两例: 例1,有10千欧的电阻若干个,每个电阻价格相同。现在某电路中需要一个15千欧的电阻,试用这些10千欧电阻设计一个满足需要,且造价最低的电路。答案是图1 如果设计成这样的电路(见图2)虽然总的阻值是15千欧,但所用10千欧电阻个数较多,造价不是最低。例2,标有“8V1.2W”的电灯需要临时给某处照明。现有电动势δ=1.5伏,内阻r=0.5欧的干电池若干 Let’s look at two examples: In Example 1, there are several 10 kΩ resistors, each with the same price. Now that a 15 kΩ resistor is needed in a circuit, try these 10 kΩ resistors to design a circuit that meets the needs and lowest cost. The answer is Figure 1. If the circuit is designed as such (see Figure 2), although the total resistance is 15 kilohms, the number of 10 kilohm resistors used is more, and the cost is not the lowest. In Example 2, lights marked with “8V1.2W” need to be temporarily illuminated. Existing electromotive force δ = 1.5 volts, internal resistance r = 0.5 ohms of dry cell