Understanding the Function of a Constant Volume Thermometer

In summary: The pressure and temperature are now known and u can use this to calculate the temperature of any other liquid by just using the triple point pressure and temp.In summary, a Constant volume thermometer uses a reference point to calculate temperature.
  • #1
orthovector
115
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Does anybody know how a Constant volume thermometer works?

I know that one of the reference points is the triple point of water, but I'm not sure how different gases are used along with this reference point to get different values of temperature for certain known processes. for instance, if oxygen gas is used to measure the BP of water...one gets a certain temperature that is close to 373.15 degrees kelvin. if nitrogen gas is used, one gets a value that is also close to 373.15 degrees kelvin...but it is different from the value from using oxygen gas.

I cannot picture what is going on...
 
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  • #2
It uses a constant volume of gas and measures the pressure so from PV=nRT you get the temperature. But the equation assumes a perfect gas so for a real gas you will get a small error because of a, the molecules of oxygen occupy real space so at 0K there is still a volume and b, there is an interaction between molecules so there is more pressure than you would expect.
 
  • #3
I know that... I just can't imagine how you would measure a process. For instance, if you want to measure the bp of water, do you place the gas bulb into the water and hear the water? And how would u take a reading of the pressure?
 
  • #4
Yes - you put the bulb in the boiling water (or ideally in the vapour just above it)
Then you measure the pressure with a separate pressure gauge attached to the bulb - normally a mercury manometer but probably with some sort of digital pressure gauge nowadays. I must admit I've only seen 'lab demonstration' type constant volume gas thermometers, not a real industrial one.
 
  • #6
how would one measure the triple point of water? as u know, triple point occurs ar specific pressure and temp.
 
  • #7
You use something called a triple point cell.This is evacuated and pure water added but the cell is not filled up., It is then left in the fridge so that some of the water freezes,you now have the triple point with ice water and water vapour in equilibrium.
 

1. What is a Constant Volume Thermometer?

A Constant Volume Thermometer is a type of thermometer that measures changes in temperature by measuring the changes in volume of a gas at a constant pressure. It is used to accurately measure small changes in temperature and is commonly used in scientific experiments and industrial processes.

2. How does a Constant Volume Thermometer work?

A Constant Volume Thermometer works by using a fixed amount of gas in a sealed container. As the temperature changes, the volume of the gas also changes, causing the pressure to change. The change in pressure is measured and converted into a temperature reading.

3. What are the advantages of using a Constant Volume Thermometer?

One of the main advantages of using a Constant Volume Thermometer is its high level of accuracy. It is also not affected by changes in atmospheric pressure, making it ideal for use in different locations. Additionally, it can measure a wide range of temperatures, from very low to very high.

4. What are the limitations of a Constant Volume Thermometer?

One limitation of a Constant Volume Thermometer is that it requires a fixed amount of gas, which can be difficult to maintain in certain environments. It also needs to be calibrated frequently to ensure accurate readings. Additionally, it may not be suitable for measuring rapid changes in temperature.

5. How is a Constant Volume Thermometer different from other types of thermometers?

A Constant Volume Thermometer differs from other types of thermometers in that it measures temperature indirectly, by measuring the changes in volume of a gas. Other types of thermometers, such as liquid-filled or bimetallic thermometers, directly measure the expansion or contraction of a substance due to temperature changes. Constant Volume Thermometers also have a high level of accuracy and can measure a wide range of temperatures.

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