(2004? Yangzhou) After studying electricity, Xiaoli designed an incubator circuit, as shown in the figure. A in the figure is the temperature sensor (reaches the set temperature

(1) When the switch is connected to 1, the circuit resistance is the smallest, and only R1 is connected to the circuit. According to the formula P=U2R, it can be seen that when the incubator circuit is working in the "high" gear, the maximum power consumption of the circuit is Pmax=90W,

R1=U2Pmax=(36V)290W=14.4Ω.

(2) When the switch is connected to 3, the three resistors are connected in series. When the circuit resistance is maximum, according to the formula P = U2R, it can be seen that the incubator circuit is in the "low" gear, and the minimum power is: P small = 45W, Then the current I is small = P is small U = 45W36V = 1.25A;

(3) When the switch is connected to 2, only the resistors R1 and R2 are connected in series to the circuit. The circuit resistance is moderate. According to the formula P = U2R, we can know: Insulation box The circuit is in the "medium" gear, and the power is P中=72W. At this time, the circuit current and the total resistance after R1 and R2 are connected in series can be found: I中=P中 U=72W36V=2A, R string=U2P中=( 36V)272W=18Ω．

Answer: (1) When S is set to position 1, the heating power is 90W, and the resistance of R1 is 14.4Ω;

(2) When S is set to position 3, The current in the circuit is 1.25A;

(3) When S is moved to position 2, it can be found that the circuit current I is 2A, and the total resistance R string after R1 and R2 are connected in series = 18Ω.