Match List 1 with List 2 and select the correct answer from the codes given below: List-1 List-2 A. ….is a device to measure intensity of radiation emitted from a body 1. Transducer B. …. Is an instrument which measures humidity directly 2. Reluctance C. A …. Is a device which converts the energy from one form to another 3. Hygrometer D. Transducer which makes use of air gap change is referred as….type 4. Radiation pyrometer Correct Answer A - 4, B - 3, C - 1, B - 2 Transducer:​ Active transducers are those which do not require any power source for their operation. They work on the energy conversion principle. They produce an electrical signal proportional to the input (physical quantity). Piezoelectric, thermocouple, and photovoltaic cell transducers all are active transducers. Hygrometer: A hygrometer is an instrument used to measure relative humidity. Humidity is the measure of the amount of moisture in the air. A psychrometer is an example of a hygrometer. ​ Radiation pyrometer: The main theory behind a radiation pyrometer is that the temperature is measured through the naturally emitted heat radiation by the body. This heat is known to be a function of its temperature. The radiation pyrometer has an optical system including a lens, a mirror, and an adjustable eyepiece. The heat energy emitted from the hot body is passed on to the optical lens, which collects it and is focused on the detector with the help of the mirror and eyepiece arrangement. Thus, the heat energy is converted to its corresponding electrical signal by the detector and is sent to the output temperature display device. The temperature of the sun is measured by using a radiation pyrometer. A transducer that makes use of air gap change is referred to as Reluctance type