Under what condition do certain crystalline substances generate minute potential differences?

Certain crystalline substances generate minute potential differences when subjected to pressure due to a phenomenon known as the piezoelectric effect. In materials that exhibit piezoelectric properties, applying mechanical stress causes a displacement of charge within the crystal structure, leading to a voltage across the material. This effect is utilized in various applications, such as sensors, actuators, and transducers, where mechanical energy is converted to electrical energy or vice versa.

Other conditions, while they can affect the properties of materials, do not typically result in the generation of electrical potential differences in the same way. For instance, heating can change the conductivity of a material but does not directly lead to a potential difference in crystalline substances. Similarly, magnetization affects magnetic materials but not necessarily in a way that generates voltage like in piezoelectric materials. Submerging in fluids may change the environment but does not inherently induce voltage generation similar to pressure application. Therefore, the piezoelectric effect is unique to pressure and explains why certain crystalline substances can generate potential differences under that specific condition.