Temperature Alert Circuit

Classical Mechanics Level 2

A thermistor is a resistor whose resistance reduces as its temperature increases.

Larry wants to make a circuit which alerts him if the temperature of the kettle becomes too high. He wants to use a thermistor for the circuit. In which of the following circuits will the speaker beep as the temperature rises?

Details:

  • The thermistor is in thermal contact with the kettle

  • The batteries used are 9V batteries. The speaker starts beeping if supplied voltage is more than 5V.

B A C

Pranshu Gaba by Pranshu Gaba , 22, India

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1 solution

Satyabrata Dash
May 22, 2018

C- 9V across speaker.(always beeps)

A- Here as the temperature increases , resistance of thermo resistor decreases. Thus the voltage across it decreases as well.(becomes lesser than 4.5 V assuming initial resistances of normal resistor and thermo resistor to be same) thus the speaker won't beep.

B - similar analogy as A.

1 Helpful 1 Interesting 0 Brilliant 0 Confused

Sir, If B has similar analogy as A, then how do we know the answer? @Pranshu Gaba , @Satyabrata Dash

Vinayak Srivastava - 10 months, 3 weeks ago

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For A Temp of thermistor increases, resistance decreases thus voltage decreases and becomes less than 4.5 v Thus no beeping

For B Temp of thermistor increases, resistance of thermistor decreases, so voltage across it decreases which implys the voltage across the resistor connected in series increases becoming greater than 4.5 or even 5V. Thus there is beeping.

Satyabrata Dash - 10 months, 2 weeks ago

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