The length of the train from the beginning of the locomotive to the end of the caboose would be considered the which?

• A. Pulse duration
• B. Wavelength
• C. Frequency
• D. Spatial pulse length

Answer: (D)

Think in terms of how a pulse is described: by its duration in time or by how far it extends in space. The length of the train from the locomotive to the caboose is a physical distance—the amount of space a pulse occupies as it travels. That makes it the spatial pulse length. It isn’t the time the pulse lasts (pulse duration), nor the distance of one cycle (wavelength), nor the number of cycles per second (frequency). If you picture the train as a single burst moving along the track, the distance covered while the pulse exists defines its spatial pulse length. In waves, this length equals the wave speed times the pulse duration, and it can also be expressed as the number of cycles times the wavelength.