ANS:A - electrical resistance

Psychrometry deals with the properties of gas-vapor mixtures, particularly air and water vapor mixtures. Humidity can be determined by the measurement of the electrical resistance of a fiber. Explanation:

1. Psychrometry:
   • Psychrometry is the study of the physical and thermal properties of gas-vapor mixtures, particularly air-water vapor mixtures.
   • It deals with various properties of moist air, including temperature, humidity, dew point, and enthalpy, and is commonly used in applications such as HVAC (heating, ventilation, and air conditioning) systems, weather forecasting, and industrial processes.
2. Humidity Measurement:
   • Humidity refers to the amount of water vapor present in the air.
   • Various methods are used to measure humidity, including psychrometers, hygrometers, and sensors.
   • One common method is based on the principle that certain materials, such as certain types of fibers, change their electrical resistance in response to changes in humidity.
   • As the humidity of the surrounding air changes, the moisture content of the fiber changes, leading to a corresponding change in its electrical resistance.
   • By measuring the electrical resistance of the fiber, the humidity of the surrounding air can be determined.
3. Other Methods:
   • While electrical resistance measurement is one method used for humidity measurement, there are other techniques as well, such as the use of capacitive sensors, gravimetric methods, and chilled mirror hygrometers.
   • These methods rely on different physical principles to measure humidity, including changes in capacitance, mass gain or loss due to water vapor adsorption or desorption, and condensation of water vapor on a chilled surface.