If the velocity of a longitudinal mode wave is 0.625 cm/microsecond at 1/2 inch below the surface, what is the velocity at 2 inches below the surface?

In ultrasonic testing, the velocity of longitudinal waves is generally consistent within a given material when the medium remains unchanged. This means that various factors such as temperature, material composition, and uniformity do not significantly alter the propagation speed of these waves over small depths within the same material.

In this scenario, the velocity at 1/2 inch below the surface is given as 0.625 cm/microsecond. Because the medium being tested has not changed between the depths of 1/2 inch and 2 inches, the speed of sound in that material remains constant. Hence, the velocity of the longitudinal wave at any depth, as long as it is within the same homogeneous material, will be the same.

Thus, the correct conclusion is that the velocity at 2 inches below the surface will remain at 0.625 cm/microsecond, the same as at 1/2 inch. The rationale lies in the characteristic of longitudinal waves in a uniform medium, which do not experience changes in velocity due to depth alone, provided other conditions are stable.