Non-Destructive Testing (NDT) Practice Test

Which of the following is true about sound waves in solids?

1. They cannot be reflected

2. They travel fastest in gases

3. They can propagate through solid materials

4. They are diminished in density

The correct answer is: They can propagate through solid materials

Sound waves in solids exhibit specific behaviors that are fundamentally different from their behavior in fluids like gases and liquids. The correct statement asserts that sound waves can propagate through solid materials. This is due to the molecular structure of solids, which allows for close packing of atoms or molecules. As sound waves pass through solids, they cause the particles to vibrate and transmit the energy of the wave. In contrast, the other options can be analyzed as follows: sound waves can indeed be reflected when they encounter boundaries or interfaces; they do not travel fastest in gases but in solids, where the close packing of particles facilitates quicker transmission of vibrations; and the phrase "diminished in density" does not accurately describe sound waves, as density pertains to mass per unit volume rather than the behavior of sound waves in terms of propagation. Thus, the ability of sound waves to propagate through solid materials is a defining characteristic of how these waves function in different mediums.