The physical layer of a network

The physical layer of a network is responsible for defining the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between communicating network systems.
It deals with the transmission and reception of unstructured raw data over a physical medium.
This layer defines details such as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, and other similar attributes that are required to transfer the raw bit stream over a physical medium between devices.
In summary, the physical layer primarily focuses on the physical aspects of transmitting data, such as electrical signals and mechanical connections.