You decide to weather-proof your home by installing a temperature alarm system.
ID: 1284438 • Letter: Y
Question
You decide to weather-proof your home by installing a temperature alarm system. If the temperature dips below a certain threshold (which you can directly input), an alarm is activated. In the accompanying circuit, a sensor (termed a thermistor) has a variable resistance. The thermistors resistance varies as the exposed temperature changes. A decrease in temperature causes the resistance of the thermistor to increase, while an increase in temperature causes the resistance of the thermistor to decrease. At some temperature, T, and for the given resistances: R1, R2, R3, and the given potential difference, +V, the measured potential difference (between points A and B) is zero. You would like to know what value for RT yields a measured potential difference (between points A and B) of zero.
explain how to approach the question and how to apply knowledge
You decide to weather-proof your home by installing a temperature alarm system. If the temperature dips below a certain threshold (which you can directly input), an alarm is activated. In the accompanying circuit, a sensor (termed a thermistor) has a variable resistance. The thermistor½s resistance varies as the exposed temperature changes. A decrease in temperature causes the resistance of the thermistor to increase, while an increase in temperature causes the resistance of the thermistor to decrease. At some temperature, T, and for the given resistances: R1, R2, R3, and the given potential difference, +V, the measured potential difference (between points A and B) is zero. You would like to know what value for RT yields a measured potential difference (between points A and B) of zero. explain how to approach the question and how to apply knowledgeExplanation / Answer
It is indeed very simple.One has to apply the balanced wheatstones bridge condition here.To know what is that go to http://en.wikipedia.org/wiki/Wheatstone_bridge
In balanced Wheatstone Bridge the potential VAB =0V ...and hence RT/R1=R3/R2
That is ,if RT=R1x(R3/R2)...VAB=0
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