# the thermodynamic scale

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#1
could someone in very simple words explain to me what is the thermodynamic scale and how is it independant of property of any particular substance??
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6 years ago
#2
(Original post by RRC)
could someone in very simple words explain to me what is the thermodynamic scale and how is it independant of property of any particular substance??
What do you mean by thermodynamic scale here?
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#3
i dont know!!my syllabus just says that i should have an understanding of the thermodynamic scale an aboslute zero
is there more than one thermodynamic scale?
(im terrible at physics so pls forgive my really stupid questions)
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6 years ago
#4
(Original post by RRC)
i dont know!!my syllabus just says that i should have an understanding of the thermodynamic scale an aboslute zero
is there more than one thermodynamic scale?
(im terrible at physics so pls forgive my really stupid questions)
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#5
A-level
0
6 years ago
#6
(Original post by RRC)
i dont know!!my syllabus just says that i should have an understanding of the thermodynamic scale an aboslute zero
is there more than one thermodynamic scale?
(im terrible at physics so pls forgive my really stupid questions)
I assume you've heard of the kelvin scale of temperature. Absolute zero is the theoretical point where all motion in a substance has stopped ( in reality this is not physically attainable for many reasons). Absolute zero doesn't depend on any substance, so that means this scale also doesn't depend on substances, unlike the Celsius or Fahrenheit scales which depend on material properties.
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#7
(Original post by Dualcore)
I assume you've heard of the kelvin scale of temperature. Absolute zero is the theoretical point where all motion in a substance has stopped ( in reality this is not physically attainable for many reasons). Absolute zero doesn't depend on any substance, so that means this scale also doesn't depend on substances, unlike the Celsius or Fahrenheit scales which depend on material properties.
i get the absolute part thankyou! but how do you measure temperature on a thermodynamic scale then?
also i read that its possible to establish a single fixed point in the thermodynamic scale how is that?
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6 years ago
#8
(Original post by RRC)
i get the absolute part thankyou! but how do you measure temperature on a thermodynamic scale then?
also i read that its possible to establish a single fixed point in the thermodynamic scale how is that?
The single fixed point is 0, from there we chose an arbitrary scale, for the Kelvin scale we chose for graduations to be the same as the centigrade scale, that's why a rise of 1 C is the same as a rise of 1K. The arbitrary point chosen for the Kelvin scale is the triple point of water. (But from a theoretical perspective another second point could have been chosen, and there is nothing intrinsically special about water, it was just the one we chose).
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6 years ago
#9
OK.

Temperature measurements in everyday occurrence is really about establishing a kinetic energy equilibrium (at the molecular and atomic level) between the measuring device and the medium trying to be measured.

For instance, a mercury thermometer measures the expansion of mercury in a tube when it is exposed to a source of thermal energy. Radiation, convection and conduction are the energy transfer mechanisms and the equilibrium of that expansion as a result is achieved when the energy gained by the mercury is balanced by the energy losses from the mercury to the surrounding environnment. (glass tube, air etc.

So temperature in everyday occurrence is all about referencing the properties of one medium to a transfer of heat energy from another. And because of that, the zero scale and scale divisions are completely arbitrary:

Farenheit scale: 0 probably refers to the point at which a brine solution freezes and 100 degrees is close to the human body natural temperature. The scale is arbitrarily divided into 100 divisions between those two points and extrapolated aove and below.

Celcius uses the same concept, but this time takes the freezing point of pure water as the zero reference and the boling point of water as the upper reference with 100 divisions in between and again extrapolated above and below those points for an extended scale.

Thermodynamic temperature is an 'absolute' scale and is independent of the properties of any given substance. It relates to the mimimum theoretical thermodynamic motion of atoms. i.e. no kinetic motional energy be it momentum or vibrational. This is the reference for absolute zero.

Because thermodynamic temperature is a ratio between two absolute temperatures T1/T2, the measurement scale (seperation defining an arbitrary degree) becomes irrelevant.

The Kelvin scale is most widely used and has become synonomous with absolute zero even though itself is an arbitrary scale using the triple-point of water and the Celcius scale extrapolated backwards to the theroetical calculated absolute zero temperature giving a result of -273.16 degrees Celcius.

So -273.16 becomes the zero reference for the Kelvin scale which is then divided in the same scale increments as the Celcius scale, giving the triple point of water as 273.16 Kelvin (0 degrees Celcius) etc.
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6 years ago
#10
(Original post by RRC)
could someone in very simple words explain to me what is the thermodynamic scale and how is it independant of property of any particular substance??
Temperatures on the thermodynamic scale are based on the theoretical physics of a heat engine working on the Carnot Cycle. (Not on the properties of any particular substance.) The idea was proposed by Kelvin, who showed that the scale obtained was identical to one based on an ideal gas.
This scale uses as a fixed point, a well defined temperature, the triple point of water, as 273.16 kelvin. This temperature is equal to 0.01 deg Celsius. Zero Celsius is 273.15 kelvin.

To understand how it's independent of the properties of any substance you need to understand the Carnot Cycle.

It might help to look up some of these bold terms on the internet.
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#11
i got it thanku soo much for the help everyone im really grateful!
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6 years ago
#12
I have to say that, unless we are all missing something, the question is a little misleading. The Kelvin scale zero and the ratios between temperatures are indeed independent of the properties of a specific substance but, as you have both pointed out, a fixed point based on the properties of a specific substance (water) is required to set up a temperature scale with fixed numbers in it.
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6 years ago
#13
(Original post by Martin Hogbin)
I have to say that, unless we are all missing something, the question is a little misleading. The Kelvin scale zero and the ratios between temperatures are indeed independent of the properties of a specific substance but, as you have both pointed out, a fixed point based on the properties of a specific substance (water) is required to set up a temperature scale with fixed numbers in it.
Agreed.
I understood the question to be referring to the fact that the scale does not require the variation in some property (length/pressure/volume etc) of any substance to measure variation in temperature.
Of course, as you say, the 2nd stage in the process of creating the scale is to define 2 fixed points. In this case zero and 273.16 degs. This does require a substance for the 273.16 point.
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