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Grade upto college level Thermal Physics

Let P3 be the pressure of the bulb of a constant-volume gas thermometer when the bulb is at the triple-point temperature of 273.16 K and let p be the pressure when the bulb is at room temperature. Given are three constant-volume gas there mometers” for A the gas is oxygen and p3=20 cm Hg; for B the gas is also oxygen but p3 = 40 cm Hg; for C the gas is hydrogen and p3 =30 cm Hg. The measured values of p for the three thermometers are pA , p8 , and pc’
(a) An approximate value of the room temperature T can be obtained with each of the thermometers using
TA =(273.16 K) (pA/20 cm Hg),
TB =(273.16 K) (pB/40 cm Hg),
TC =(273.16 K) (pC/30 cm Hg).
Mark each of the following statements true or false: (1) With the method described, all three thermometers will give the same value of T. (2) the two oxygen thermometers will agree with each other but not with the hydrogen thermometer. (3) Each of the three will give a different value of T. (b) In the event that there is a disagreement among the there thermometers, explain how you would change the method of using them to cause all three to give the same value of T.

Profile image of Amit Saxena
11 Years agoGrade upto college level
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1 Answer

Profile image of Askiitians Tutor Team
ApprovedApproved Tutor Answer1 Year ago

To tackle your question, let's break it down into two parts: analyzing the statements regarding the constant-volume gas thermometers and discussing how to align their measurements. We'll start with the first part, where we evaluate the truth of each statement based on the provided equations for temperature.

Evaluating the Statements

We have three thermometers, each using different gases and different pressures at the triple-point temperature. The equations for calculating room temperature (T) are:

  • TA = (273.16 K) × (pA/20 cm Hg)
  • TB = (273.16 K) × (pB/40 cm Hg)
  • TC = (273.16 K) × (pC/30 cm Hg)

Now, let's analyze each statement:

Statement 1: All three thermometers will give the same value of T.

This statement is false. Each thermometer uses a different reference pressure (20 cm Hg, 40 cm Hg, and 30 cm Hg) for the same temperature. Therefore, unless the pressures pA, pB, and pC are specifically adjusted to yield the same ratio with their respective reference pressures, the calculated temperatures will differ.

Statement 2: The two oxygen thermometers will agree with each other but not with the hydrogen thermometer.

This statement is also false. While both thermometers A and B use oxygen, they have different reference pressures (20 cm Hg and 40 cm Hg). Unless the pressures pA and pB are adjusted to yield the same ratio with their respective reference pressures, they will not necessarily agree. The hydrogen thermometer (C) will also likely yield a different temperature due to its different reference pressure.

Statement 3: Each of the three will give a different value of T.

This statement is true. Given the different reference pressures and the fact that the pressures pA, pB, and pC are not specified to be equal, it is reasonable to conclude that each thermometer will provide a different value for room temperature.

Aligning the Measurements

In the event of disagreement among the thermometers, a method to ensure they provide the same value of T involves standardizing the reference conditions. Here’s how you could approach this:

  • Calibration: Use a known temperature standard, such as the triple point of water, to calibrate each thermometer. Adjust the readings of pA, pB, and pC so that they correspond to the same reference pressure.
  • Adjusting Pressures: If possible, adjust the pressures in each thermometer to a common reference point. For example, you could set all three to a pressure of 30 cm Hg and measure the corresponding temperatures.
  • Using a Common Gas: If feasible, use the same gas for all thermometers. This would eliminate discrepancies due to different gas properties and ensure that the thermometers respond similarly to temperature changes.

By implementing these strategies, you can minimize discrepancies and achieve consistent temperature readings across all thermometers. This approach highlights the importance of calibration and standardization in experimental measurements.