The wavelength of an ultrasonic wave is:

• A. Directly proportional to velocity and frequency
• B. Directly proportional to velocity and inversely proportional to frequency
• C. Inversely proportional to velocity and directly proportional to frequency
• D. Equal to the product of velocity and frequency

Answer: (B)

Wavelength is determined by the basic wave relation v = f λ, where v is the speed of the wave in the medium, f is its frequency, and λ is the wavelength. Solving for wavelength gives λ = v / f, which shows that wavelength increases with higher propagation speed and decreases with higher frequency. In practice, for a fixed medium, doubling the frequency halves the wavelength, while a faster medium increases the wavelength for the same frequency. This is why the statement describing wavelength as directly proportional to velocity and inversely proportional to frequency is the correct one.