If a pulse contains a fixed number of cycles, increasing frequency will cause pulse duration to?

If a pulse contains a fixed number of cycles, increasing frequency will cause pulse duration to?

• A. Decrease
• B. Increase
• C. Stay the same
• D. Oscillate

Answer: (A)

When a pulse is defined by a fixed number of cycles, the total duration depends on how long each cycle lasts. The period of one cycle is the reciprocal of frequency, 1/f, so the pulse duration is the number of cycles times the period: duration = N × (1/f) = N/f. Therefore, increasing frequency while the number of cycles stays the same makes the total pulse duration shorter. For example, a 5-cycle pulse lasts longer at 1 MHz than it does at 5 MHz. The other options don’t fit because longer cycles or more cycles would be needed to increase duration, a constant duration would require frequency not to change, and oscillation isn’t involved when the number of cycles is fixed.

When a pulse is defined by a fixed number of cycles, the total duration depends on how long each cycle lasts. The period of one cycle is the reciprocal of frequency, 1/f, so the pulse duration is the number of cycles times the period: duration = N × (1/f) = N/f. Therefore, increasing frequency while the number of cycles stays the same makes the total pulse duration shorter. For example, a 5-cycle pulse lasts longer at 1 MHz than it does at 5 MHz. The other options don’t fit because longer cycles or more cycles would be needed to increase duration, a constant duration would require frequency not to change, and oscillation isn’t involved when the number of cycles is fixed.