Tracking temperature Monitoring of temperatures in electronic devices is often a

Question

Tracking temperature Monitoring of temperatures in electronic devices is often accomplished using thermistors, circuit elements whose resistance varies rapidly with temperature. The actual circuits are more complicated than the one at right, hut it illustrates the basic principle. As the temperature of the thermistor rises, its resistance drops; a small rise in temperature leads to a large drop in resistance. At 25 Degree C, the thermistor has a resistance of 3.0 Ohms. As the temperature rises to 60 Degree C the resistance drops to 200 Ohms. This changcs the voltage measured by the meter-an electrical quantity that can be easily monitored. What is the reading on the voltmeter at 25 Degree C? What is the reading on the voltmeter at 60 Degree C?

Explanation / Answer

a) at 25 degrees r = 3 k ohm

   current i= v/r = 10/5000 = 0.002 amp

voltmeter readding at 25 degrees = ir = 0.002 x200 = 0.4 volt

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b)
at 60 degrees= i = v/r = 10/2200 = 0.0045 amp

voltmeter reading = v = ir = 0.9 volts

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