In view of different thermometers, the following statements are given. Identify the correct statement (s)

Thermocouples are often used to measure rapidly varying temperatures. These devices consist of two different conductive materials joined together at one end, which generate a voltage when there's a temperature difference between the junctions.

They're commonly employed in various applications where fast temperature changes occur, like in industrial settings, manufacturing, or scientific experiments. Thermocouples are known for their rapid response to temperature changes, making them suitable for measuring fluctuating temperatures accurately and swiftly.

Vapor pressure thermometry, which relies on the relationship between temperature and the vapor pressure of a liquid or solid, can indeed be used to measure very low temperatures. This method is based on the principle that at a given temperature, substances have a characteristic vapor pressure, and this pressure changes predictably with temperature.

At low temperatures, certain substances have very low vapor pressures, making them suitable for measuring these extreme cold conditions. For instance, helium-3 and helium-4 are commonly used in dilution refrigerators, and their vapor pressure-temperature relationship is utilized to measure temperatures very close to absolute zero.

For a constant volume gas thermometer, the gas is usually filled at a low pressure and at a temperature that can be precisely controlled or measured.

The reason for filling the gas at a low pressure is to ensure that the gas behaves ideally, meaning it follows the ideal gas law more accurately. At low pressures, the gas molecules have less interaction with each other, minimizing deviations from ideal gas behavior.

Additionally, filling the gas at a high temperature is beneficial for several reasons:

1. **Expanded Range:** High-temperature gas allows for a wider temperature range to be measured accurately. This is because it ensures that even at lower temperatures, the gas won't condense or liquefy, affecting the volume and pressure relationship.

2. **Linear Behavior:** A higher initial temperature provides a wider span of temperatures to work with. The relationship between temperature and pressure (according to Charles's Law for a constant volume gas) tends to be more linear over a broader range at higher initial temperatures.

3. **Reduced Error:** Operating at higher temperatures can reduce errors caused by instrumental limitations or inaccuracies. Precise control and measurement become more manageable in comparison to extremely low temperatures.

So, filling a constant volume gas thermometer with gas at low pressure and high temperature helps ensure better adherence to ideal gas behavior and allows for a wider and more linear temperature range for accurate measurements.