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Perhaps I can add another example. The air inside a running microwave oven, radio wave oven, induction cooker, laser oven, may show different temperature measurement value, depending on the thermometer type used.
For some systems- far from equilibrium- the temperatures can be different- or even negative.
Temperature is still only meaningful if a system is at equilibrium.
Quote from: Bored chemist on 31/03/2022 08:56:42Temperature is still only meaningful if a system is at equilibrium.How do you define equilibrium?Imagine a frozen pond in a winter. The depth is 10 meters. The air temperature above the surface is -10°C. One meter ice layer has been formed on the surface. The rest of the pond is still liquid water. This condition hasn't changed for a week. Is it in equilibrium?
The air inside a running microwave oven, radio wave oven, induction cooker, laser oven, may show different temperature measurement value, depending on the thermometer type used.
For objects that are not ideal gas, their temperature can be defined as the same as the ideal gas which don't exchange energy with them when they are in contact
Practical methods to measure temperature, such as used in mercury and alcohol thermometer, bimetal, thermocouple, RTD, and infrared thermometer are less reliable, involve non-linearity, and have narrower range and use case.
Quote from: Bored chemist on 31/03/2022 08:56:42For some systems- far from equilibrium- the temperatures can be different- or even negative.The concept of negative temperature is interesting but AFAIK it can never be more than a concept.
No. The temperature of the air (assuming it is well stirred and thus in internal equilibrium) has a unique value.
We know, by definition, the temperature of water at its triple point.It isn't an ideal gas,
That's a definition of one value for a temperature for one type of macroscopic system. It doesn't provide a whole scale of temperature
This might be helpful.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4865254/
It (the triple point of water) (together with the definition of absolute zero) is the only fixed point on the whole of the Kelvin temperature scale.
Quote from: hamdani yusuf on 31/03/2022 10:46:58Quote from: Bored chemist on 31/03/2022 08:56:42Temperature is still only meaningful if a system is at equilibrium.How do you define equilibrium?Imagine a frozen pond in a winter. The depth is 10 meters. The air temperature above the surface is -10°C. One meter ice layer has been formed on the surface. The rest of the pond is still liquid water. This condition hasn't changed for a week. Is it in equilibrium?No. It can't be at eqm because it has a temperature gradient.That's because heat is flowing from the Earth's core, into the water, up through the ice and out again.
Quote from: hamdani yusuf on 31/03/2022 03:28:31The air inside a running microwave oven, radio wave oven, induction cooker, laser oven, may show different temperature measurement value, depending on the thermometer type used.No. The temperature of the air (assuming it is well stirred and thus in internal equilibrium) has a unique value. The practical problem is that the power source interacts differently with different types of thermometer and if you aren't careful you end up measuring the microwave absorbtivity of a thermocouple or whatever, or even generating a load of sparks and no data. An external thermistor bolometer is probably the simplest practical device for an industrial oven but even then you need to ensure that the emissivity of the air is greater than that of the oven itself - quite difficult to do. If the oven is ventilated, you could put a glass bottle gas thermometer inside and measure the pressure of the working volume of air, which will be close to that of its ambient. If it isn't ventilated, than a pressure gauge will give you the answer.
If I put thermometers at the bottom, middle, and top of the pond, they would show certain values. Are they meaningless?
In a microwave oven, the thin metal in the bolometer can absorb the radiation and generate heat, which may exceed the air temperature inside the oven chamber.
Only a fool would put anything but a gas thermometer inside a microwave oven to measure the air temperature.
Most people are more interested in the wall temperature,
The engineer who lives inside my head wants to ask why you are interested in the air temperature inside an oven.
Most people are more interested in the wall temperature
Not really.https://www.amazon.co.uk/Brannan-Microwave-Thermometer/dp/B005RDUSAW
This a Meat thermometer , has metal skewer , there are no instructions. and look on Makers site , No trace of this product?Answer:The metal skewer is to make a hole in meat etc to enable the thermometer to be inserted more easily. You don't put the thermometer IN the microwave - you simply use it to check the temperature of the foods you have cooked in there.
always read the small print:
Bit of a sensitive point as, in a former incarnation, I was asked to review the draft European Directive on Physical Hazards which would have prevented the construction of any oven that could accommodate a human