Which statement about the axial resolution formula AR ≈ (n × c) / (2f) is true?

• A. It shows AR is inversely proportional to c
• B. It shows AR is independent of f
• C. It shows AR is inversely proportional to n
• D. It shows AR is directly proportional to c and inversely proportional to f

Answer: (D)

Axial resolution relates to the wavelength and how many acoustic cycles are used. The form AR ≈ (n × c) / (2f) shows that AR scales with the speed of sound c and with the number of cycles n, and it decreases as frequency f increases (since higher f means shorter wavelength λ = c/f). The factor 1/2 is just a constant and doesn’t change the relationships.

So, stating that AR is directly proportional to c and inversely proportional to f matches the formula. It also helps to remember that AR also grows with n, but that detail doesn’t contradict the shown relationships. The other options conflict with the formula: AR isn’t inversely related to c, it isn’t independent of f, and it isn’t inversely related to n.