What does a large difference between the temperature of a dry bulb thermometer and the wet-bulb thermometer of a hygrometer denote?

Hint: The device used to measure the moisture content in air, soil, and confined spaces are known as a hygrometer. There are different types of hygrometers like classical thermometers, hair tension hygrometers, and modern electronic hygrometers.

Complete Answer:
The hygrometer measures the moisture content. The type of hygrometer discussed here is also called a psychrometer. The principle of its working is evaporative cooling. It has two bulbs: a wet-bulb thermometer and a dry bulb thermometer. If a large difference is recorded between the temperature of a wet-bulb thermometer and the dry bulb thermometer of a hygrometer, it simply denotes that the relative humidity is low. In dry air, relative humidity is low and the evaporation rate is higher. If a small difference is recorded between the temperature between the wet-bulb thermometer and dry bulb thermometer of a hygrometer, it can be inferred that the relative humidity is high. In humid air, the relative humidity is high and the rate of evaporation is lower than that on a dry day. Mechanical hygrometers work on the principle that organic substances, especially finer substances like hair expand and contract rapidly on heating and cooling. This contracting and expanding hair element changes the tension in the spring that moves the needle of the dial.

Note: There are two more types of hygrometers namely electrical hygrometer and dew point hygrometer. The electrical hygrometer usually measures the change in resistance of a semiconductor device with a change in humidity. While the dew point hygrometer comprises a polished mirror that cools at constant pressure and humidity content.