Which of the following devices can be used to detect radiant heat? (1) Liquid thermometer (2) Six's maximum and minimum thermometer (3) Constant volume air thermometer (4) Thermopile
(4) Thermopile Explanation: Based on the thermoelectric effect, the thermopile can be used as a heat sensor to measure thermal radiation. A thermopile is made of thermocouple junction pairs connected electrically in series. Thermocouples near the ground measures radiant energy.