Final answer:
The subject of this question is Physics, specifically the study of energy and matter interactions. In this context, the electromagnetic field mentioned in the question is a topic in physics, particularly in the subfield of electromagnetism.
Step-by-step explanation:
A water heater consists of a cylinder that is composed of two sections.
The first one is embedded in perfectly insulated material and is subjected to an electromagnetic field that induces.
Physics is the subject that deals with the study of energy and matter and their interactions.
In this context, the electromagnetic field mentioned in the question is a topic in physics, particularly in the subfield of electromagnetism.