Ch. 26 26.(III) You are designing a wire resistance heater to heat an enclosed volume of gas. For the apparatus to function properly, this heater must transfer heat to the gas at a very constant rate. While in operation, the resistance of the heater will always be close to the value 0,RRbut may fluctuate slightly causing its resistance to vary a small amount RD 0R.To maintain the heater at constant power, you design the circuit shown in Fig. 26–44, which includes two resistors, each of resistance r. Determine the value for rso that the heater power will remain constant even if its resistance Rfluctuates by a small amount. [Hint:If 0,Dthen 0dPPR.dRDD<0] [Solution] The goal is to determine rso that 00.RdPdRThis ensures that Rproduce very little change in ,RPsince .RRdPPRdRThe power delivered to the heater can be found by 2heaterheater,PVRand so we need to determine the voltage across the heater.
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