Sling psychrometer is used for measuring –
**Core Concept**
A sling psychrometer is a device used to measure the **humidity** of the air, specifically the **dew point**. It works on the principle that the rate of evaporation of water from a wet wick is influenced by the humidity of the surrounding air.
**Why the Correct Answer is Right**
The sling psychrometer consists of a dry thermometer and a wet thermometer attached to a rotating frame. As the frame is rotated, the air is rapidly moved over the thermometers, causing the wet thermometer to evaporate water and cool down at a faster rate than the dry thermometer. By comparing the readings on the two thermometers, the humidity can be calculated. This is based on the concept that the rate of evaporation of water is higher in dry air and lower in humid air.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a sling psychrometer is not used to measure temperature directly, but rather to infer humidity from the temperature difference between the wet and dry thermometers.
**Option B:** This option is incorrect because a sling psychrometer is not a type of hygrometer that uses a chemical indicator to measure humidity.
**Option C:** This option is incorrect because a sling psychrometer is not a device used to measure atmospheric pressure.
**Clinical Pearl / High-Yield Fact**
A sling psychrometer is a simple and effective tool for measuring humidity, but it requires careful calibration and handling to obtain accurate results. It is commonly used in field settings, such as in weather forecasting or in industrial settings where humidity levels need to be monitored.
**Correct Answer: D. Humidity measurement.