If a 5 MHz wave is traveling in the tissues listed below, which will have the longest wavelength?

If a 5 MHz wave is traveling in the tissues listed below, which will have the longest wavelength?

• A. fat
• B. air
• C. muscle
• D. bone

Answer: (D)

Wavelength at a fixed frequency depends on how fast sound travels in the medium. Since λ = c/f, a higher speed of sound (c) yields a longer wavelength for the same frequency. Among the listed tissues, bone carries the fastest speed of sound (roughly 4,000 m/s), while fat and muscle are around 1,450–1,540 m/s and air is much slower (about 343 m/s). Therefore, at 5 MHz, bone has the longest wavelength (about 0.8 mm), with fat and muscle near 0.29–0.31 mm and air around 0.07 mm.

Wavelength at a fixed frequency depends on how fast sound travels in the medium. Since λ = c/f, a higher speed of sound (c) yields a longer wavelength for the same frequency. Among the listed tissues, bone carries the fastest speed of sound (roughly 4,000 m/s), while fat and muscle are around 1,450–1,540 m/s and air is much slower (about 343 m/s). Therefore, at 5 MHz, bone has the longest wavelength (about 0.8 mm), with fat and muscle near 0.29–0.31 mm and air around 0.07 mm.