What is physically displaced in a crystal due to an electrical current that produces pressure?

The principle behind the displacement in a crystal due to an electrical current relates to the movement of charged particles, specifically ions, within the crystal structure. When an electrical current flows through a crystal, it can cause ions—atoms or molecules that carry a positive or negative charge—to migrate from their original positions. This displacement of ions leads to changes in the physical structure of the crystal, which can generate pressure.

This phenomenon underlies various applications, including piezoelectricity, where certain materials generate an electric charge in response to mechanical stress or, conversely, change shape when subjected to an electric field. The relationship between the electrical current, ion movement, and the resultant pressure is a key aspect of understanding the behavior of ionic crystals under electrical influences.

The other options do not accurately describe the process in this context. Electrons are carriers of charge, but they do not physically displace the structure of a crystal in the same way that ions do. Photons are particles of light and do not involve physical displacement within a crystal structure due to electric current. Molecules may refer to larger groups of atoms that could potentially experience relative motion, but in terms of the specific response to electric current and pressure generation in a crystal lattice, ions are the primary participants.