Electronics Question

[Dominatorrr]

OK, so there's this circuit to be used in a spa to provide a warning that the temperature has exceeded 60 degrees. There is a thermistor and variable resistor in the circuit. The V-OUT to activate the siren is taken over the thermistor. The siren will only sound if there is 3V or more across it. The battery attached to the circuit is 5V.

The Temperature vs Resistance graph for the Thermistor shows a curved line with a negative gradient (thus meaning that as the temperature increases the resistance decreases).

I actually don't get how this circuit functions. As the temperature increases the resistance of the thermistor decreases and thus it will take less and less of the voltage so how will the siren sound if it needs more than 3V across it? Wouldn't this mean that at low temperatures the siren would sound? There is nothing to say that the variable resistor automatically decreases its resistance or something?

[StumbleBum]

If you have all the information right then i'd say the question as a whole is a mistake because your right in saying that it will receive less and less voltage across it.

And also a variable resistor does not automatically decrease it has to be set by the user before any circuit is used, the term variable resistor merely means that it can be varied.