Two ideal gas thermometers A and B use oxygen and hydrogen respectively. The following observations are made:
| Temperature | Pressure thermometer A | Pressure thermometer B |
|---|---|---|
| Triple-point of water | Pa | Pa |
| Normal melting point of sulphur | Pa | Pa |
What is the absolute temperature of normal melting point of sulphur as read by thermometers A and B?
Temperature read by Thermometer A = 392.69 K. Temperature read by Thermometer B = 391.98 K.
What do you think is the reason behind the slight difference in answers of thermometers A and B? (The thermometers are not faulty). What further procedure is needed in the experiment to reduce the discrepancy between the two readings?
The slight difference arises because oxygen and hydrogen are real gases, not ideal gases. They deviate slightly from ideal gas behaviour. To reduce the discrepancy, the experiment should be conducted at lower gas densities (lower pressures), as all gases at low densities exhibit the same expansion behaviour.
Explanation
This question tests the understanding of ideal gas thermometers. For an ideal gas thermometer, temperature T is proportional to pressure P at constant volume: T = T_tr × (P/P_tr), where T_tr = 273.16 K is the triple point of water. The slight difference in readings occurs because real gases deviate from ideal behaviour, and this deviation decreases at lower densities.