Power supply voltage U = IR = 0.2A×(50+10) Ohm = 12V.
(2) The number of ammeters is 0.4A, and the total resistance of the circuit is R'= 12/0.4 = 30 ohms.
So in this semiconductor resistor: R'= 30- 10 = 20 ohms.
The table shows that when the resistance of the semiconductor is 20 ohms, the ambient temperature is 40℃.