ARDMS SPI Acoustic Waves and Properties 2 — Questions and Answers
Question 1: Which acoustic parameter is determined solely by the medium through which sound travels?
- Frequency
- Propagation speed (Correct answer)
- Amplitude
- Period
Correct answer: Propagation speed
Propagation speed depends entirely on the medium's density and stiffness, not on the sound source.
Question 2: If the propagation speed of sound increases while frequency remains constant, what happens to wavelength?
- Wavelength decreases
- Wavelength stays the same
- Wavelength increases (Correct answer)
- Wavelength becomes zero
Correct answer: Wavelength increases
Wavelength = propagation speed / frequency, so an increase in speed with constant frequency results in a longer wavelength.
Question 3: The acoustic impedance of a tissue is defined as the product of:
- Frequency and wavelength
- Density and propagation speed (Correct answer)
- Amplitude and frequency
- Attenuation and depth
Correct answer: Density and propagation speed
Acoustic impedance (Z) = density (ρ) × propagation speed (c), measured in Rayls.
Question 4: Rarefaction in a longitudinal acoustic wave refers to:
- A region of increased particle density
- A region of decreased particle density (Correct answer)
- The peak amplitude of the wave
- The point of maximum pressure
Correct answer: A region of decreased particle density
Rarefaction is the low-pressure, low-density phase of a longitudinal wave where particles are spread apart.
Question 5: Which unit is used to quantify acoustic intensity?
- Watts per square centimeter (W/cm²) (Correct answer)
- Pascals (Pa)
- Decibels (dB)
- Rayls
Correct answer: Watts per square centimeter (W/cm²)
Acoustic intensity represents power per unit area and is expressed in W/cm² or mW/cm².
Question 6: In diagnostic ultrasound, increasing the frequency of the transducer will:
- Increase penetration depth and decrease resolution
- Decrease penetration depth and increase axial resolution (Correct answer)
- Increase both penetration and resolution
- Have no effect on penetration or resolution
Correct answer: Decrease penetration depth and increase axial resolution
Higher frequency shortens wavelength, improving axial resolution, but also increases attenuation, reducing penetration depth.
Question 7: The period of a sound wave is the reciprocal of:
- Wavelength
- Propagation speed
- Amplitude
- Frequency (Correct answer)
Correct answer: Frequency
Period (T) = 1 / frequency (f); a 1 MHz wave has a period of 1 microsecond.
ARDMS SPI Acoustic Waves and Properties 2
Which acoustic parameter is determined solely by the medium through which sound travels?