1

New Theories / Re: what is temperature?

« on: Today at 14:19:52 »

Here's another thought experiment to check our understanding of temperature, and its relationship with entropy.
Two isolated containers each with 1 cubic meter volume. Their internal surface is perfectly elastic, thus doesn't absorb energy from molecules hitting it. A small pipe equipped with a closed valve is connecting those containers. Initially, the first container contains helium gas at STP, while the second container is at vacuum. The whole system is inside a space lab, isolated from outside  world.
When the valve is opened, some gas molecules will move to the second container. Since the collision with the container walls are elastic, they maintain their kinetic energy. At equilibrium, the flow rate from the first container equals the reverse flow. The pressure of both containers become half of standard pressure. The temperature is still at standard temperature, according to ideal gas law, P.V=n.R.T
The gas, which initially occupied 1 cubic meter of volume, now occupy 2 cubic meter.

Why do you keep posting stuff that we clearly already know?

By the way, if you say "an ideal gas" rather than "helium", you can get round the problem that it isn't actually ideal.

2

New Theories / Re: what is temperature?

« on: Today at 14:18:20 »

But, in principle, your spinning magnet warms it up a bit.

The effects are much less than Eddy current generated in metals, thus doesn't significantly change the temperature measurement.

The experiment in the video clearly shows this.

Eddy Current Demo #electromagnetic induction #physics #physicsninja

That's a lot of trouble to go to in order to show that you don't know what the phrase "in principle" means.

3

New Theories / Re: what is temperature?

« on: Today at 14:17:09 »

But we know that glass melts at its melting temperature.

We know that the melting point of something (when it has one- glass doesn't) is defined as the temperature where the liquid and solid phases are in equilibrium.

4

New Theories / Re: what is temperature?

« on: 09/01/2025 12:31:46 »

And, if it's not at equilibrium, it doesn't have a properly defined temperature.

If that's the case, the curve below won't be possible because the temperature is measured while heat is being transferred to/from the system.

If you look carefully, you will se the only bits of the line where the temperature is constant are the bits where there are two phases in equilibrium.

It will melt before reaching equilibrium.

I know.

And it would melt

Why do you keep posting stuff that we clearly already know?

5

New Theories / Re: what is temperature?

« on: 09/01/2025 12:20:12 »

According to Kirchhoff's law of thermal radiation, a good absorber is also a good emitter for the same radiation frequency.

There's a good chance that I told you about Kirchhoff's radiation law. I have cited it quite a bit in these pages.

6

New Theories / Re: what is temperature?

« on: 08/01/2025 23:48:53 »

On teh other hand...

Note that objects heated by radiation from incandescent lamps can have higher temperature than the glass surface of the lamps. This pose question about thermal contact. Is exchange of kinetic energy through radiation counted as thermal contact?

It does not pose that question.

If you put a mirror round the bulb so that all the radiation was reflected back then the glass would  reach thermal equilibrium with the filament. (And it would melt)
But a bit like the Calender and Barnes continuous flow water calorimeter, the heat is continuously carried away from the glass (by the air round it, and by emission of IR) , so it never reaches the same temperature as the filament.
It never reaches equilibrium.


Paradoxically, even though quartz glass is nearly opaque to far IR radiation quartz halogen lamps were sometimes used as the "light" source for far IR spectroscopy.
The radiation used was actually that emitted from the quartz envelope.

7

New Theories / Re: what is temperature?

« on: 08/01/2025 23:31:32 »

I spent several years working on "dynamic equilibrium" calorimeters for measuring ionising radiation dose rates. Long story but it was a cunning way of measuring millidegree temperature changes to better than 0.1% precision.

The classic Callendar and Barnes continuous flow water calorimeter uses a similar principle.

So... not Joule's method.
You found a method where the temperature difference between ingoing and outbound  was essentially constant.
OK.
I agree it's a very clever method.

It seems to be drifting rather from the point (so far as HY's threads ever have one)

8

New Theories / Re: what is temperature?

« on: 07/01/2025 17:52:45 »

If the magnet is spinning then viscous dag will heat the air near to it.
And then it won't be at equilibrium any more.

We tend to consider the boundary layer a stationary in laminar viscous flow. And it would be a pity if Joule's determination of the mechanical equivalent of heat by stirring water was seriously wrong - his result was within 0.75% of the current value.

Joule measured the rate of rise of temperature.
Funny looking eqm that's getting hotter with time.

9

New Theories / Re: what is temperature?

« on: 07/01/2025 10:29:20 »

But you seem un\aware of the fact that a spinning magnet in air will heat the air, thus disturbing the equilibrium.

You seem to be unaware that as an example, I put the spinning magnet inside a vacuum glass box. There will be no friction between the air and the spinning magnet. But the spinning magnet can still generate heat in nearby metals by inducing Eddy current.

I'm unaware of many things that you just decided to make up. Mindreading isn't my forte.
You should have mentioned it.


You do know that oxygen is paramagnetic, don't you?

And, if it's not at equilibrium, it doesn't have a properly defined temperature.

Does the surface of the sun have a properly defined temperature?
Does the corona of the sun have a properly defined temperature?

Fairly well defined. But, in principle, your spinning magnet warms it up a bit.
Why do you ask?

10

New Theories / Re: what is temperature?

« on: 03/01/2025 23:00:36 »

Being unaware of these effects can lead to erroneous measurement values.

And the guy who can tell you about 5 different sorts of liquid in glass thermometers is almost certainly not "unaware of these effects".
But you seem un\aware of the fact that a spinning magnet in air will heat the air, thus disturbing the equilibrium.
And, if it's not at equilibrium, it doesn't have a properly defined temperature.

What point did you think you were making, and to whom?

11

New Theories / Re: what is temperature?

« on: 03/01/2025 22:57:00 »

Depends on the radiated peak power, and is only limited by the horizon.

Pick one.
But...
"Common sense says that the air close to the spinning magnet will be  in thermal equilibrium with the magnet surface"
Not really; but the problem lies with the definition of the problem.
If the magnet is spinning then viscous dag will heat the air near to it.
And then it won't be at equilibrium any more.

12

Just Chat! / Re: What Happened To 'Ye'?

« on: 02/01/2025 16:58:44 »

Like I said before on this board, using the singular form of you (which is thee and thou in English) fell out of use a couple hundred years ago.

A lot of folk in the North of England don't agree with that assessment; and they sometimes use  "ye" too.

13

Just Chat! / Re: What is the best way to crash land a plane?

« on: 01/01/2025 23:20:38 »

"What is the best way to crash land a plane?"
Remotely
https://en.wikipedia.org/wiki/2012_Boeing_727_crash_experiment

14

New Theories / Re: what is temperature?

« on: 01/01/2025 12:50:53 »

No. They both show the temperature of the contents of the thermometer bulb. One is heated entirely by conduction from the air, one has an additional dynamo component.

How can we measure the temperature of the air around the spinning magnet?

We get a bunch of thermometers.
It would be a dumb choice but, just to make the point, we can use a mercury thermometer, an alcohol thermometer a gallium thermometer, a water thermometer  and a hexane thermometer.
And then we measure the electrical conductivity of the filling liquids.
We can plot the apparent temperature against the electrical conductivity of the filling liquid and then we can extrapolate to zero conductivity.

Science has been doing that sort of thing for centuries.
As I have said before, you should try learning it.

15

New Theories / Re: what is temperature?

« on: 01/01/2025 12:43:15 »

Long-range radar generally works in the kHz to MHz range where water vapor absorption is minimal.

In clear air, what's the typical range of microwave radar?

16

New Theories / Re: what is temperature?

« on: 31/12/2024 15:25:00 »

Your result would presume that the target volume was effectively a black body but I guess the behavior of air below 2.4 GHz is a good approximation.

Better guesses are available.
In particular, better guesses should be available to anyone whose field of interest includes radar which depends on microwaves travelling through air for long distances.

17

New Theories / Re: what is temperature?

« on: 29/12/2024 22:11:13 »

Thermistors work from around -50C to 300C. I have used them to measure temperature changes of 1mK to +/- 1μK. If you want a traceable calibration in the room temperature range, no real problem - use an oil bath and a platinum resistor to fix absolute points to better than 0.05K

You will need reflector in infrared range instead of microwave.

So, for example, aluminium foil instead of aluminium foil.

18

Just Chat! / Re: What is the best way to crash land a plane?

« on: 28/12/2024 20:16:39 »

A runway at an airport.

19

New Theories / Re: what is temperature?

« on: 26/12/2024 17:48:46 »

No. They both show the temperature of the contents of the thermometer bulb. One is heated entirely by conduction from the air, one has an additional dynamo component.

How can we measure the temperature of the air around the spinning magnet?

Are you asking an actual question, or do you plan to go down a pointless rabbit hole about the impossibility of measuring a system without perturbing it?

20

New Theories / Re: what is temperature?

« on: 24/12/2024 23:13:46 »

For example, a mercury thermometer and alcohol thermometer can show different values when measuring temperature of the air around a spinning magnet.

The  mercury thermometer will not be showing the temperature of the air, will it?
Most bits of measuring equipment can be misused.
So what?