Describe how a psychrometer works.?

Answer 1

A psychrometer indirectly measures humidity in the air by the temperature difference shown by two liquid bulb-and-capillary type thermometers, one with a wetted bulb and one dry. A "sling psychrometer" is the usual version; this has the two thermometers mounted on a board that is connected by a pivot to a handle. The user spins the board which provides a relative air flow that speeds up both thermometers reaching their final value. Tables and/or formulas convert the wet- and dry-bulb readings to relative humidity. See the ref.