Non-Destructive Testing (NDT) Practice Test

What can be said about the velocity of sound traveling through a given material?

1. Velocity varies with temperature

2. Velocity is affected by frequency

3. Velocity remains constant

4. Velocity decreases with thickness

The correct answer is: Velocity remains constant

The velocity of sound traveling through a given material is indeed influenced by various factors, but one of the fundamental characteristics is that for a specific material under consistent conditions, the velocity of sound can be considered constant. This constancy arises from the material's inherent properties, such as density and elastic modulus, which determine how sound waves propagate through it. While it is true that velocity can vary with temperature and can be influenced by factors like the material's state or composition, within a stable environment where temperature, density, and other conditions remain unchanged, the speed of sound for that specific material remains uniform. Moreover, frequency does not affect the velocity of sound in a particular medium; rather, it influences the wavelength. Similarly, the notion that velocity decreases with thickness is not correct, as the thickness of a material does not change how fast sound travels through it but may affect attenuation or the intensity of the sound wave as it passes through. Understanding these fundamentals assists in applying concepts of sound propagation in materials within the context of Non-Destructive Testing.