Question

In a fire alarm system, a thermistor T has a resistance of 2000Ω at room temperature. Its
resistance decreases as the temperature increases. The alarm is triggered when the potential
difference between X and Y reaches 4.5V. What is the resistance of the thermistor when the alarm is triggered?

Answer 1

picture of the circuit.

Answer 2

@TheSmartOne @pooja195 @whpalmer4

Answer 3

Are you asking generally or just the three you've quoted ?

Answer 4

The attached may help ... bon chance
http://perendis.webs.com

Answer 5

asking anybody who can help really. nobody was replying so i just tagged the few physics people i spotted on the homepage lol

Answer 6

but thanks a lot! i had completely forgotten about that formula

Answer 7

It's the formula for a voltage divider, and it saves the boredom of grinding through Ohm's law. But it helps a lot if you know how to derive it.
Other thing about the circuit is that OK, the alarm trips at 4.5V, but it doesn't show how the alarm is made to trip. I think that this could be the realms of a circuit called a "Schmitt trigger", which is, as with many other circuits, based on a comparison of two voltages. If the reference voltage is set at 4.5V, when the XY voltage reaches that, the trigger triggers and triggers the circuit for the alarm. And one place there are comparators is inside "OPERATIONAL AMPLIFIERS".