National Physical Therapy Examination (NPTE) Practice Exam

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What is the duty cycle percentage for pulsed wave ultrasound set at 2 msec on time and 8 msec off time?

The correct answer is: 20%

To determine the duty cycle percentage for pulsed wave ultrasound, one needs to calculate the ratio of the "on time" (the time the ultrasound is emitting) to the total time of one cycle (the sum of on time and off time). In this scenario, the "on time" is given as 2 milliseconds (msec) and the "off time" is 8 msec. To find the total time of one cycle, you simply add these two values together: Total time = On time + Off time = 2 msec + 8 msec = 10 msec. Next, to find the duty cycle percentage, you divide the "on time" by the total time and then multiply by 100 to convert it to a percentage: Duty cycle = (On time / Total time) × 100 = (2 msec / 10 msec) × 100 = 20%. Thus, the duty cycle percentage is 20%. This reflects that during 20% of the total cycle time, ultrasound energy is being delivered, which can play a crucial role in therapeutic ultrasound applications by controlling the intensity and heating effects on the tissues being treated.