The LC circuit mainly consists of capacitors and inductors, which oscillate freely through the mutual conversion of electric field energy and magnetic field energy. To maintain oscillation, an amplification circuit with positive feedback is required. LC oscillators are divided into transformer coupled and three-point oscillators. Many quartz crystal oscillators are used, and LC oscillators composed of integrated operational amplifiers are also used. Due to the fact that the parameters of the device cannot be exactly the same, the states of the two transistors change at the moment of power on. This change, due to the increasingly strong positive feedback effect, leads to reaching a temporary steady state.

In 1847, Joule designed a more ingenious experiment by placing water in a calorimeter, installing a rotating shaft with blades in the middle, and then letting a descending weight drive the blades to rotate. Due to the friction between the blades and water, both the water and the calorimeter heated up. Based on the height of the heavy object falling, the converted mechanical work can be calculated; Based on the temperature rise of water in the calorimeter, the increase in internal energy of water can be calculated. By comparing two numbers, the accurate value of thermal energy equivalent can be obtained.