Figure A is an automatic control device designed by Xiaoping for air conditioning in school office buildings, and R is a thermistor. The relationship between resistance and temperature is shown in the

Figure A is an automatic control device designed by Xiaoping for air conditioning in school office buildings, and R is a thermistor. The relationship between resistance and temperature is shown in the following table. (1) With the increase of indoor temperature, the resistance of thermistor decreases and the current in control circuit increases. When the current reaches 15mA, the armature is attracted, the resistance of the right air conditioner circuit increases, the current decreases, and the air conditioner starts to work. When the temperature drops, the resistance of the control circuit increases and the current decreases to a certain value, so that the air conditioning circuit is disconnected, thus realizing automatic control.

(2) Resistors R and R 0 are connected in series in the circuit. As can be seen from the table, at 25℃, the resistance R = 390Ω, R0 =10Ω,

So the total resistance r is always = r+r0 = 390ω+ 10ω = 400ω,

The current in the circuit I = ur = 6V400ω = 0.015a =15ma,

That is, 15mA should be marked with 25℃, as shown in the following figure;

So the answer is: (1) With the increase of indoor temperature, the resistance of thermistor decreases and the current in control circuit increases. When the current reaches 15mA, the armature is attracted, the resistance of the right air conditioning circuit increases, the current decreases, and the air conditioner starts to work. When the temperature drops, the resistance of the control circuit increases and the current decreases to a certain value, so that the air conditioning circuit is automatically disconnected.

(2) The position at 25℃ on the dial is 15mA, as shown in the above figure;