Understanding the Hypsometer for Altitude Determination

The question asks about an instrument used for determining altitude based on the principle that the boiling point of water changes with atmospheric pressure. Let's look at the options provided.

Different instruments are designed for various types of measurements. The working principle mentioned in the question is key to identifying the correct instrument.

• Hypsometer: A hypsometer is an instrument used to measure altitude. Its operation is directly based on the fact that the boiling point of water decreases as atmospheric pressure decreases. Since atmospheric pressure generally decreases with increasing altitude, measuring the boiling point of water allows one to determine the altitude.
• Durometer: A durometer is an instrument used to measure the hardness of a material, typically polymers, elastomers, and rubbers. It has no relation to altitude, boiling point, or atmospheric pressure.
• Bubble tube: A bubble tube is a component used in various surveying instruments, such as levels and theodolites. It contains a liquid and an air bubble and is used for leveling, meaning determining whether a surface or line is horizontal. It does not measure altitude directly based on boiling point.
• Barometer: A barometer is an instrument used to measure atmospheric pressure. While atmospheric pressure is related to altitude (pressure decreases as altitude increases), a standard barometer measures pressure directly using mercury or an aneroid mechanism. The question specifically mentions the variation of the boiling point of water with atmospheric pressure as the working principle for determining altitude, which is the principle behind a hypsometer, not a standard barometer.

Therefore, the instrument whose working for determining altitudes depends on the fact that the temperature at which water boils varies with atmospheric pressure is the hypsometer.