1.
What is the SI unit of acoustic impedance?
Correct Answer
B. Pascal-second per cubic meter
Explanation
Acoustic impedance is a measure of the resistance to the transmission of sound waves through a medium. It is defined as the product of the density of the medium and the speed of sound in that medium. The SI unit of acoustic impedance is the pascal-second per cubic meter (Pa·s/m³). This unit represents the resistance offered by a unit volume of the medium to the propagation of sound waves. It is derived from the basic units of pressure (pascal, Pa) and volume (cubic meter, m³), reflecting the pressure gradient required for sound wave propagation.
2.
Acoustic impedance depends on which of the following properties?
Correct Answer
D. All of the above
Explanation
Acoustic impedance depends on various properties such as temperature, material density, and sound frequency. Temperature affects the speed of sound in a medium, material density influences the resistance offered by the medium, and sound frequency determines the wavelength and energy of the sound waves. All these factors collectively contribute to the overall acoustic impedance of the medium.
3.
Which of the following materials has the highest acoustic impedance?
Correct Answer
C. Steel
Explanation
Steel has a high density and high speed of sound compared to other materials like water, air, and wood. This combination of properties results in the highest acoustic impedance among the options provided. Steel's high acoustic impedance makes it an effective barrier to the transmission of sound waves, which is why it is commonly used in applications where sound isolation or insulation is required.
4.
What happens to the acoustic impedance when the density of a material increases?
Correct Answer
A. Increases
Explanation
Acoustic impedance increases when the density of a material increases because higher density leads to greater resistance to the transmission of sound waves. As the density of a material increases, the molecules become closer together, making it more difficult for sound waves to propagate through the medium. This increased resistance results in higher acoustic impedance, reflecting the material's ability to impede the transmission of sound.
5.
The speed of sound in a medium is directly proportional to what property?
Correct Answer
C. Density
Explanation
The speed of sound in a medium is directly proportional to its density. This relationship is described by the equation v = √(K/ρ), where v is the speed of sound, K is the bulk modulus (a measure of the medium's resistance to compression), and ρ is the density of the medium. Therefore, higher density leads to higher acoustic impedance, as denser materials require more energy to transmit sound waves due to their greater resistance to compression.
6.
In which medical imaging technique is acoustic impedance utilized?
Correct Answer
C. Ultrasound
Explanation
Acoustic impedance is utilized in ultrasound imaging to differentiate between tissues based on their density and composition. Ultrasound waves are partially reflected at interfaces between tissues with different acoustic impedances. By analyzing the reflection patterns, ultrasound imaging can produce detailed images of internal structures, allowing for the diagnosis of various medical conditions.
7.
Which of the following materials has the lowest acoustic impedance?
Correct Answer
C. Air
Explanation
Air has the lowest density and speed of sound among the options provided, resulting in the lowest acoustic impedance. This is because air molecules are relatively far apart, allowing sound waves to propagate with minimal resistance. As a result, air is often used as a reference medium when discussing acoustic impedance and is assigned a value close to zero.
8.
What does a higher acoustic impedance mismatch lead to at an interface?
Correct Answer
A. Increased reflection
Explanation
A higher acoustic impedance mismatch at an interface leads to increased reflection of sound waves. When sound waves encounter an interface between two mediums with different acoustic impedances, part of the wave is transmitted into the second medium, while the rest is reflected back into the first medium. The degree of reflection depends on the magnitude of the impedance mismatch. A higher mismatch results in more reflection, as more energy is unable to pass through the interface and is instead reflected back.
9.
What happens to acoustic impedance as the speed of sound increases?
Correct Answer
B. Decreases
Explanation
As the speed of sound increases, the time taken for sound to propagate through a material decreases. This decrease in propagation time indicates that the material offers less resistance to the transmission of sound waves. Since acoustic impedance is a measure of this resistance, an increase in the speed of sound corresponds to a decrease in acoustic impedance. Therefore, when the speed of sound increases, the acoustic impedance decreases.
10.
What is the approximate value of acoustic impedance of air?
Correct Answer
D. 0.0004 kg/m^2s
Explanation
The approximate value of the acoustic impedance of air is around 0.0004 kg/m^2s. Air has a relatively low density and speed of sound compared to other materials, resulting in a low acoustic impedance value. This value is commonly used as a reference point in discussions of acoustic impedance and is essential for various applications in acoustics and sound engineering.
11.
What property determines the amount of reflection at an interface?
Correct Answer
C. Acoustic impedance
Explanation
The amount of reflection at an interface is determined by the acoustic impedance mismatch between the two media involved. When two materials with different acoustic impedances meet, a portion of the sound wave is reflected back into the first medium, while the rest is transmitted into the second medium. The degree of reflection depends on the difference in acoustic impedance between the two materials. A higher mismatch leads to more significant reflection, while a lower mismatch results in less reflection.
12.
Which of the following statements is true about acoustic impedance?
Correct Answer
C. It is the product of material density and speed of sound.
Explanation
Acoustic impedance is calculated as the product of material density and the speed of sound in that material. Mathematically, it is represented as Z = ρc, where Z is the acoustic impedance, ρ is the density of the material, and c is the speed of sound in that material. This relationship highlights the importance of both density and speed of sound in determining the resistance offered by a medium to the transmission of sound waves.
13.
In ultrasound imaging, what does acoustic impedance matching aim to reduce?
Correct Answer
B. Reflection
Explanation
Acoustic impedance matching in ultrasound imaging aims to reduce reflection of sound waves at tissue boundaries. By minimizing reflections, the imaging system can produce clearer and more detailed images of internal structures. Acoustic impedance matching is achieved by using coupling agents or specialized transducer designs to optimize the transmission of ultrasound waves into the body and minimize the loss of energy at tissue interfaces.
14.
What factor affects the propagation of sound waves but not acoustic impedance?
Correct Answer
D. Frequency
Explanation
While the propagation of sound waves is affected by frequency, acoustic impedance specifically refers to the resistance to the transmission of sound waves through a medium. Frequency determines the pitch or tone of a sound but does not directly impact the medium's ability to impede the transmission of sound waves. Therefore, while frequency affects the behavior of sound waves, it is not a factor in determining acoustic impedance.
15.
How does acoustic impedance change when the speed of sound decreases?
Correct Answer
B. Decreases
Explanation
Acoustic impedance decreases when the speed of sound decreases because lower speed means less resistance to the transmission of sound waves. Acoustic impedance is calculated as the product of material density and the speed of sound in that material. Therefore, a decrease in the speed of sound leads to a decrease in acoustic impedance, indicating that the material offers less resistance to the propagation of sound waves.