The time-of-flight is ______ related to the depth that sound pulse travels.

• A. Inversely related
• B. Directly related
• C. Not related
• D. Exponentially related

Answer: (B)

Time-of-flight is directly related to depth in a uniform medium. The pulse must travel to the target and back, so the total distance is twice the depth. With a constant speed of sound, time = distance/speed, meaning the time increases in direct proportion to how deep the target is. In other words, deeper targets take proportionally longer to return a echo. A quick check: if depth doubles, the time-of-flight doubles as well (time = 2×depth / speed). The formula depth = (speed × time)/2 captures this linear relationship. If the medium’s speed varied, or there were refractions, the relationship could be more complex, but in a steady medium it’s a straight, direct link.