Please look at attached photo. Tracking Temperature Monitoring of temperatures i

Question

Please look at attached photo.

Tracking Temperature Monitoring of temperatures in electronic devices is often accomplished using thermistors, circuit elements whose resistance varies rapidly with temperature. The actual circuits arc more complicated than the one at right, but 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 degreeC, the thermistor has a resistance of 3.0 k Ohm. As the temperature rises to 60 degreeC, the resistance drops to 200 ohm. This changes the voltage measured by the meter-an electrical quantity that can be easily monitored. What is the reading on the voltmeter at 25 degreeC? What is the reading on the voltmeter at 60 degreeC?

Explanation / Answer

Part I ) At 25o C net resistance = 2k+3k= 5kohms (series connection)

Net current in the cicuit will be given by

I=V/R

Where I is the current

V is the voltage

R is the resistance

Hence I=10/5000=2*10-3 A

Hence voltage across thermistor will be I*Rth= 6V

Part II )

At 60o C net resistance = 2k+0.2k= 2.2kohms (series connection)

Net current in the cicuit will be given by

I=V/R

Hence I=10/2200=4.54*10-3 A

Hence voltage across thermistor will be I*Rth= 0.91V

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