Non-Destructive Testing (NDT) Practice Test

How do sound waves propagate within a material?

1. Due to heat expansion

2. Through vibrations of the medium's particles

3. By external force applied

4. Through electronic signals only

The correct answer is: Through vibrations of the medium's particles

Sound waves propagate through a material primarily by the vibrations of the medium's particles. When a sound wave travels through a solid, liquid, or gas, it causes the particles within that medium to vibrate and oscillate. These vibrations create areas of compression and rarefaction, which allow the sound energy to move through the material. The efficiency of sound propagation can vary based on the material's density, elasticity, and structure, but the fundamental principle remains that it's the particle-to-particle interaction that facilitates the transmission of sound. The other options involve concepts that do not accurately describe the mechanism of sound wave propagation. For instance, heat expansion does not directly cause sound waves to travel; however, it might affect the properties of the material itself. External force can initiate vibrations, but it does not encompass the continuous propagation of sound waves once they have been generated. Electronic signals pertain to a different realm entirely, related more to data transmission and communication rather than mechanical wave propagation.