What is the piezoelectric effect?

The piezoelectric effect refers to the phenomenon where certain materials, particularly crystals, generate an electrical charge when they are mechanically deformed or subjected to an external force. This effect arises due to the displacement of charges within the crystal lattice when the material is stressed, leading to a separation of positive and negative charges and resulting in an electric voltage.

Option B accurately describes this process, emphasizing the mechanical vibration of a crystal in response to an applied voltage. This voltage can lead to physical displacement or vibration of the crystal, showcasing the interplay between electrical and mechanical energy. The piezoelectric effect is widely used in various applications, including sensors, actuators, and transducers, further demonstrating its significance in technology.

The other options do not align with the definition of the piezoelectric effect. The electrical vibration of a spring does not involve the properties of piezoelectric materials. Magnetic response in a wire coil relates to electromagnetic induction, while thermal expansion of a metal deals with temperature effects rather than mechanical movement related to electrical properties. Thus, these alternatives do not capture the essence of the piezoelectric phenomenon as accurately as the selected answer.