Damping reduces which of the following?

• A. Pulse duration
• B. Spatial pulse length
• C. Both pulse duration and spatial pulse length
• D. Neither pulse duration nor spatial pulse length

Answer: (C)

Damping causes the pulse to decay quickly as it travels, so the wave contains fewer cycles and the tail dies out sooner. Since pulse duration is the time span of those cycles, fewer cycles means a shorter pulse duration. Spatial pulse length is the distance the pulse occupies, which is the number of cycles in the pulse times the wavelength ( SPL = cycles × λ ). The wavelength is set by frequency and the medium, so damping mainly reduces the number of cycles, thereby shortening SPL as well. In short, damping both shortens how long the pulse lasts and how long it extends in space.