An understanding of this important relationship has led to the development of many valuable inventions. In the field of medicine, MRI scans, are another new discovery based on the principle of electromagnetism and the phenomenon that nuclei of some atoms line up in the presence of an electromagnetic field. They are able to show a complete three dimensional picture of the interior structure of the body, and are extremely valuable in hospitals. The study of heat is called thermodynamics. Physicist study how heat can be changed into work, how it is produced, how it is transferred from one place to another, and how it changes matter.
Heat ranks as one of the most important kinds of energy that is used.
The knowledge that physicists gain from the study of heat and how it acts, aids in making use of heat energy to warm homes, cook foods, and run machines. Atomic and Nuclear Physics have revealed many of the secrets of matter. Knowledge gained from the study of nuclear physics has released the greatest energy known on earth, the energy of the atom. Solid State Physics supplied information that led to such developments as the transistor and the solar battery. It involves the study of the physical properties and atomic structure of solids, particularly of crystals.