Which statement correctly expresses the relationship to compute wavelength in a solid when frequency is known?

• A. Wavelength equals velocity times frequency
• B. Wavelength equals velocity squared divided by frequency
• C. Wavelength equals frequency divided by velocity
• D. Wavelength equals velocity divided by frequency

Answer: (D)

Wavelength comes from how far a wave travels in one cycle. In a solid, the wave speed is the velocity at which the ultrasonic wave moves through that material, and the frequency tells how many cycles occur each second. The relationship that links them is λ = v / f. This makes intuitive sense: increasing speed lets more distance pass in the same time, so a cycle stretches over a longer distance, while increasing frequency means more cycles in the same distance, so each cycle is shorter. The units confirm it too: velocity is meters per second and frequency is cycles per second, so their ratio gives meters, a length. If you multiply speed by frequency, you’d get meters per second squared; if you divide frequency by velocity, you’d get reciprocal meters; neither matches a wavelength. The division form v / f yields the correct wavelength. For example, if v = 5000 m/s and f = 2 MHz (2,000,000 Hz), λ = 5000 / 2,000,000 = 0.0025 m = 2.5 mm.