Which statement is true about thermometers?

Which statement is true about thermometers?

• A. Wet-bulb temperature readings are always higher than dry-bulb thermometers.
• B. Dry-bulb thermometers are used to measure both temperature and humidity.
• C. Wet-bulb thermometers measure the temperature when the bulb is dry.
• D. Dry-bulb thermometers protect the bulb from moisture.

Answer: (D)

Understanding how dry-bulb and wet-bulb thermometers work helps explain why moisture matters for accurate readings. A dry-bulb thermometer is used to measure the actual air temperature and its reading should reflect the surrounding air without being influenced by moisture on the sensor. If the bulb gets wet or damp, evaporation or condensation can skew the measurement, so it’s kept dry as part of the measurement setup. The wet-bulb thermometer, on the other hand, has a wick around its bulb that is kept moist; as air passes over it, evaporation cools the bulb and lowers the temperature reading, which provides information about humidity when compared with the dry-bulb reading. Because the dry-bulb reading must represent true air temperature without moisture affecting it, the idea that dry-bulb thermometers protect the bulb from moisture captures this essential point. The other statements don’t fit the roles: wet-bulb readings are not typically higher than the dry-bulb (they’re usually lower due to evaporative cooling), a dry-bulb thermometer does not measure humidity, and the wet-bulb bulb is not dry by design.

Understanding how dry-bulb and wet-bulb thermometers work helps explain why moisture matters for accurate readings. A dry-bulb thermometer is used to measure the actual air temperature and its reading should reflect the surrounding air without being influenced by moisture on the sensor. If the bulb gets wet or damp, evaporation or condensation can skew the measurement, so it’s kept dry as part of the measurement setup. The wet-bulb thermometer, on the other hand, has a wick around its bulb that is kept moist; as air passes over it, evaporation cools the bulb and lowers the temperature reading, which provides information about humidity when compared with the dry-bulb reading. Because the dry-bulb reading must represent true air temperature without moisture affecting it, the idea that dry-bulb thermometers protect the bulb from moisture captures this essential point. The other statements don’t fit the roles: wet-bulb readings are not typically higher than the dry-bulb (they’re usually lower due to evaporative cooling), a dry-bulb thermometer does not measure humidity, and the wet-bulb bulb is not dry by design.