PHYSICS CH.3 REVIEW: DESCRIBING SOUND WAVES

True. Ultrasound is defined as any wave with a frequency greater than 20,000 hertz. 15,000 MHz is a frequency or 15,000,000,000 Hz!

T or F? A wave with a frequency of 15,000 MHz is ultrasound.

False. Intensity is proportional to the amplitude squared. If we triple the amplitude, we increase the intensity by a factor of nine.

T or F? If the amplitude of a wave is increased to 3 times its original value, the intensity is increased by 6 times.

False. Intensity is the power of beam divided by its cross-sectional area. If we halve the power, we will halve the intensity.

T or F? If the power of a wave is halved, the intensity is reduced to one-fourth its original value.

True

T or F? Propagation speed and frequency are unrelated.

False. Speed and frequency are unrelated.

T or F? Propagation speed increases as frequency decreases.

False. Propagation speed is determined by the medium only. Frequency and speed are unrelated.

T or F? Propagation speed increases as frequency increases.

False. Speed and frequency are unrelated.

T or F? Propagation speed increases as frequency increases.

inversely

acoustic velocity and compressibility

inversely

acoustic velocity and density

directly

amplitude and intensity

directly

amplitude and power

inversely

elasticity and speed of sound

unrelated

frequency and intensity

inversely

frequency and period

unrelated

frequency and sound speed

directly

stiffness and sound speed

C. 10 cm/ 2 cm= 5 cm/sec

A sound beam travels a total of 10 cm in 2 seconds. What is the speed of the sound? A. 10 cm/sec B. 2 cm/sec C. 5 cm/sec D. 0.2 cm/sec

Parameters are determined by: 1. both 2. sound source 3. sound source 4. medium 5. sound source 6. sound source 7. sound source

Does the medium or the sound source determine these parameters? 1. wavelength 2. frequency 3. intensity (initial) 4. propagation speed 5. period 6. power (initial) 7. amplitude (initial)

B. Recall that intensity equals power divided by area. If intensity remains unchanged, then whatever happens to power must also happen to area. In this case, power has doubled. Therefore, area must have doubled as well.

If intensity remains the same while the power is doubled, what has happened to the beam area? A. quadrupled B. doubled C. halved D. unchanged

C. 0.2 W/cm^2

If the power in a beam is 1 watt and the area is 5 cm^2, what is the beam's intensity? A. 5 W/cm^2 B. 1 W/cm^2 C. 0.2 W/cm^2 D. 1 watt

Medium 1. Since both media have the same stiffness, the medium with the greater density has the lower propagation speed.

Medium 1 has a density of 9 and a stiffness of 6. Medium 2 has a density of 8 and a stiffness of 6. In which medium will sound travel slower?

Acoustic propagation properties

The effects of a medium on an ultrasound wave are called ____________.

Bioeffects

The effects of sound waves on tissue in the body are called ____________.

Acoustic propagation properties

The effects of tissue on sound waves are called _____________.

E. mm represents the units for distance.

What is the wavelength of a wave with an unknown frequency traveling in soft tissue? A. 0.51 us B. 0.51 m/s C. 0.51 pascals D. 0.51 watts E. 0.51 mm

The following can or cannot be changed: 1. cannot 2. cannot 3. can 4. cannot 5. cannot 6. can 7. can

Using a particular ultrasound system and transducer, which of the following cannot be changed by the operator? 1. wavelength 2. frequency 3. intensity 4. propagation speed 5. period 6. power 7. amplitude (initial)

units are as follows: 1. millimeters 2. hertz 3. Watts/cm^2 4. meters/second 5. second 6. Watts

What are the units of: 1. wavelength 2. frequency 3. intensity 4. propagation speed 5. period 6. power

B. In soft tissue, wavelength equals 1.54 mm divided by the frequency in MHz. Thus, 2 MHz sound will have a wavelength of 0.77 mm.

What is the wavelength of 2 MHz sound in soft tissue? A. 1.54 mm B. 0.77 mm C. 0.51 mm D. 1.54 km/s E. 3.08 mm

C. In soft tissue, wavelength equals 1.54 mm divided by the frequency in MHz. Thus, 3 MHz sound will have a wavelength of 0.51 mm.

What is the wavelength of 3 MHz sound in soft tissue? A. 0.51 m B. 0.51 km C. 0.51 mm D. 0.51 nm E. 0.51 um

A, E. (frequency, period)

Which of the following are considered acoustic parameters? A. frequency B. density C. distance D. pressure E. period

B, C, F. (density, particle motion, and pressure)

Which of the following are considered acoustic variables? A. Frequency B. density C. particle motion D. temperature E. period F. pressure

B. Speed is inversely proportional to density and directly proportional to stiffness.

Which of the following characteristics will create the fastest speed of sound? A. high density, high stiffness B. low density, high stiffness C. high density, low stiffness D. low density, low stiffness

C. Speed is inversely proportional to density and directly proportional to stiffness.

Which of the following characteristics will create the slowest speed of sound? A. high density, high stiffness B. low density, high stiffness C. high density, low stiffness D. low density, low stiffness

unrelated

power and frequency

directly

power and intensity

inversely

wavelength and frequency

unrelated

wavelength and intensity