Today's Word of the Day means...
radiometer ra·di·om·e·ter (rā'dē-ŏm'ĭ-tər)
A device that measures the intensity of radiant energy, consisting of a partially evacuated glass bulb containing lightweight vertical vanes, each blackened on one side, suspended radially about a central vertical axis to permit their revolution about the axis as a result of incident radiation.
An instrument that detects electromagnetic radiation.
A device for determining the penetrative power of x-rays.
A device used to detect or measure radiation. Radiometers generally consist of a glass bulb containing a rarefied gas in which four diamond-shaped paddles are mounted on a central axis. Each paddle is black on one side and silvery on the other. When radiation such as sunlight strikes them, the black side absorbs radiation and the silvery side reflects it, resulting in a temperature difference between the two sides and causing motion of gas molecules around the edges of the paddles. This motion of the surrounding gas molecules causes the paddles to spin. Precision radiometers, which use a complete vacuum rather than a gas, exploit the difference in radiation pressure on either side of the paddles to cause them to spin. Radiometers measure the intensity of radiation by measuring the rate of spin of the paddles. Also called light mill.
instrument for detecting or measuring radiant energy. The term is applied in particular to devices used to measure infrared radiation. Radiometers are of various types that differ in their method of measurement or detection. Those that function by means of an increase in the temperature of the device, such as Herschel's thermometer, are called thermal detectors. Commonly used thermal detectors include the thermocouple, which produces a voltage when heated, and the bolometer, which undergoes a change in electrical resistance when heated. Devices that can, in principle, detect a singular quantum of radiant energy, such as Becquerel's photographic plate, are called quantum detectors. The photoelectric cell is the basis of many current quantum detectors.