Which statement describes short pulses?

• A. Many cycles in the pulse
• B. Longer wavelengths
• C. Longer listening time
• D. Fewer cycles in the pulse

Answer: (D)

Short pulses are defined by having fewer cycles within the emitted burst. The duration of a pulse is roughly the number of cycles it contains times the period of each cycle, so using fewer cycles makes the pulse shorter. That’s why describing a pulse as having fewer cycles best fits a short pulse, and why the other ideas don’t describe it: many cycles would create a longer pulse, longer wavelengths relate to lower frequency (not the pulse duration itself), and longer listening time refers to the measurement window after emission rather than the pulse content. Shorter pulses also tend to have a broader bandwidth, which helps with better axial resolution in imaging.