What is the ratio of on time to total time of a pulsed wave emitter?

• A. Duty Factor (DF = PW X PRF)
• B. Peak Power
• C. Average Power
• D. Exposure Duration

Answer: (A)

The main concept is the duty factor, which tells you how much of each cycle the emitter is actually on. In a pulsed system energy is produced only during the pulse width (on-time) and not during the rest of the cycle (off-time). The fraction of time the device is on is t_on divided by the total cycle time T. Since T is the period between pulses (T = 1/PRF) and t_on is the pulse width (PW), this ratio becomes PW × PRF. Expressed as a fraction (or percentage), this is the duty factor.

This quantity links directly to average power: average power equals peak power multiplied by the duty factor, because you’re weighting the on-time power by how often the system is actually on. The other terms describe different things—the peak power is the instantaneous power during a pulse, and exposure duration is the total time of exposure, not the on/off ratio.