一、(16分)小明利用学校实验室的电磁继电器、热敏电阻 R_1、可变电阻器 R_2等器件设计了一个恒温箱控制电路,如图1所示.其中“交流电源”是恒温箱加热器的电源(加热器在恒温箱内,图中未画出);R_1处于恒温箱内,图2是小明通过实验测得 R_1的阻值随温度变化的关系曲线;电磁继电器的电源两端电压U=6V,电磁继电器线圈的电阻可不计,通过实验测得当电流为30 mA 时,电磁继电器的衔铁被吸合. I. (16 points) Xiao Ming used a school laboratory’s electromagnetic relay, thermistor R_1, variable resistor R_2 and other devices to design a thermostat box control circuit, as shown in Figure 1. The “AC power supply” is a constant temperature Box heater power supply (heater in the incubator, not shown in the figure); R_1 is in the constant temperature box, Figure 2 is the relationship between the resistance value of R_1 and the temperature change measured by Xiaoming through experiments; The terminal voltage U = 6V, the resistance of the electromagnetic relay coil can not be counted, through the experiment measured when the current is 30 mA, the armature of the electromagnetic relay is attracted.