Joule law demonstrator

The utility model discloses a Joule law demonstrator which belongs to an experiment demonstrating instrument for middle-school physics teaching, and is an air constant-pressure thermometer composed of a closed vessel provided with electric heating wires, and a glass tube horizontally arranged. A bottom board, a graduated scale and the glass tube of a phenomenon displaying part are transparent bodies so that a projector is conveniently used for amplifying the phenomenon displaying part. The closed vessel is additionally provided with an air inlet and outlet nozzle. The closed vessel is opened when numbers are read in experiments, and the air pressure in the vessel is immediately exchanged with outside through the air inlet and outlet nozzle so that the air pressure on both ends of a liquid column is equal and stop moving. The utility model successfully solves the problems of poor quantitative performance, difficult reading, large error and small experiment-phenomenon visibility existing in Joule law experiments.