The length of space over which one cycle occurs is known as the:

• A. Duty factor
• B. Wavelength
• C. Spatial pulse length
• D. Pulse repetition frequency

Answer: (B)

The concept being tested is the relationship between a cycle and the distance it travels in space. The length of space over which one complete cycle occurs is defined as the wavelength. It’s the spatial distance from one point in a wave (for example, a crest) to the next identical point, representing how far the wave travels in one cycle. In ultrasound terms, wavelength equals the speed of sound in tissue divided by the frequency, so higher frequency means a shorter wavelength.

That’s why this option is the best choice: it directly describes the spatial distance covered by a single cycle of the wave.

The other terms describe different ideas. Duty factor is about how much of the time the pulse is on during a cycle, a temporal measure rather than a spatial one. Spatial pulse length refers to the actual length in space of an entire transmitted pulse, which can contain multiple cycles, not just one cycle. Pulse repetition frequency is a rate—the number of pulses emitted per second—not a spatial distance.