If a 5 MHz wave travels through tissues such as fat, air, muscle, and bone, which will have the shortest wavelength?

If a 5 MHz wave travels through tissues such as fat, air, muscle, and bone, which will have the shortest wavelength?

• A. Fat
• B. Air
• C. Muscle
• D. Bone

Answer: (B)

Wavelength depends on the speed of sound in the medium, and with the same frequency, slower media produce shorter wavelengths. Air has the slowest speed among the options (about 343 m/s), so it yields the shortest wavelength: roughly 343 m/s divided by 5,000,000 Hz ≈ 6.9 × 10^-5 meters, or about 70 micrometers. Fat, muscle, and bone have higher speeds (≈1450, 1580, and 4000 m/s, respectively), giving longer wavelengths around 0.29 mm, 0.32 mm, and 0.80 mm. Thus, air results in the shortest wavelength at 5 MHz.

Wavelength depends on the speed of sound in the medium, and with the same frequency, slower media produce shorter wavelengths. Air has the slowest speed among the options (about 343 m/s), so it yields the shortest wavelength: roughly 343 m/s divided by 5,000,000 Hz ≈ 6.9 × 10^-5 meters, or about 70 micrometers. Fat, muscle, and bone have higher speeds (≈1450, 1580, and 4000 m/s, respectively), giving longer wavelengths around 0.29 mm, 0.32 mm, and 0.80 mm. Thus, air results in the shortest wavelength at 5 MHz.