ARDMS Ultrasound Physics & Instrumentation Practice Exam

Which of the following statements about power is NOT true?

1. Power is proportional to the square of the amplitude

2. Power varies with frequency

3. Power remains the same as amplitude increases

4. Power decreases with increased distance

The correct answer is: Power remains the same as amplitude increases

The statement that power remains the same as amplitude increases is not true. Power in an ultrasound wave is directly proportional to the square of the amplitude of the wave. This means that when the amplitude increases, the power must increase as well. In ultrasound physics, power can be described mathematically as \( P \propto A^2 \), where \( P \) is power and \( A \) is amplitude. This relationship indicates that if the amplitude doubles, the power increases by a factor of four. Therefore, claiming that power remains constant while amplitude increases contradicts this fundamental principle. The other statements are indeed accurate. Power does vary with frequency, particularly in relation to how energy is transmitted through tissue. Additionally, as sound waves travel through a medium, the intensity (and thus power) decreases with increased distance due to the spreading of the wavefront and attenuation effects.