How Does a Hot Wire Ammeter Achieve Thermal Equilibrium?

[Samar A]

In my textbook it says:"in the hot-wire ammeter

the pointer stands at a definite reading when the temperature of platinum-iridium becomes constant and the wire stops expanding. That is achieved when the rate of heat radiated by the platinum-iridium wire becomes equal to the rate of heat generated in it."
I actually don't understand the phrase: "the rate of heat radiated by the platinum-iridium wire becomes equal to the rate of heat generated in it" could you please clarify it for me?

 

[anorlunda]

actually don't understand the phrase: "the rate of heat radiated by the platinum-iridium wire becomes equal to the rate of heat generated in it" could you please clarify it for me?

It is really the same thing as saying that the temperature stops changing.

$I^2 R$ losses generate heat in the wire. The hot wire looses heat to the air around it. When the two are not balanced, temperature changes.

 

[Averagesupernova]

Interesting. I had not seen the hot wire ammeter mentioned anywhere for many many years. I always thought it was a clever setup in an as-simple-as-possible way.

 

[Samar A]

Interesting. I had not seen the hot wire ammeter mentioned anywhere for many many years. I always thought it was a clever setup in an as-simple-as-possible way.

We study AC circuits in our physics assignment this year, and we studied how the moving coil ammeter works to measure the intensity of the DC, but it couldn't measure it for an AC, so we should know about the hot-wire ammeter.
I noticed the same too while searching on the internet. The hot wire ammeter is not mentioned so much, and there aren't a lot of explanations about how it works.

 

[cnh1995]

We study AC circuits in our physics topics this year, and we studied how the moving coil ammeter works to measure the intensity of the DC, but it couldn't measure it for an AC, so we should know about the hot-wire ammeter.
I noticed the same too while searching on the internet. The hot wire ammeter is not mentioned so much, and there aren't a lot of explanations about how it works.

The amount of heat generated in the wire in a particular time is proportional to the square the rms current through it. I think this is the principle used while calibrating hot wire meters. RMS value is also called as 'heating' value.

You will study moving iron type meters where the driving torque is proportional to the square of the current. They are preferred over hot wire meters now-a-days for measurement of ac quantities

 

[Samar A]

The amount of heat generated in the wire in a particular time is proportional to the square the rms current through it. I think this is the principle used while calibrating hot wire meters. RMS value is also called as 'heating' value.

Yes, exactly, that is the principle used. But what confused me is that there is a heat generated and a heat radiated. I don't know if there will be an equilibrium so that the wire stops expanding or what it meant by saying that the rate of heat generated becomes equal to the rate of heat radiated.

You will study moving iron type meters where the driving torque is proportional to the square of the current. They also are used for measurement of ac quantities.

That seems interesting I didn't know about this instrument yet, but looking forward to know about it in the future, anyway.