physics chapter 3 back of book questions

The frequency of a continuous acoustic wave is 5 MHz. The wave is then pulsed with a duty factor of 0.1. What is the new frequency? A. 0.5 B. 0.5 MHz C. 5 MHz D. 10 MHz

C. Frequency is the recipical

What is characteristic of acoustic waves with frequencies of less than 20 Hz when compared with waves having frequencies of more than 20 Hz? A. they travel less effectively in soft tissue. B. they travel more rapidly C. the attenuate more when traveling in soft tissue D. humans cant hear them

D. Waves with frequencies of less than 20 kHz are inaudible to humans and are called infrasonic. They travel at the same speed as waves with higher frequencies and attenuate at a lesser rate than waves with higher frequencies.

True or false, with standard ultrasound pulses, the frequency of the ultrasound changes significantly as the wave propagates through the body.

False. In diagnostic imaging, the frequency of the sound wave generally remains constant and does not routinely change as the sound propagates through the body. Slight changes in frequency occur when sound strikes moving structures. This forms the basis for Doppler ultrasonography.

What determines the period of an ultrasound wave? A. the transducer B. the medium through which the sound travels C. both A. and B. D. neither A. nor B.

A. The sound source (the transducer) that produces an acoustic signal determines the period of a wave. The wave's period is unrelated to the medium through which the sound travels, and will not change as the wave moves from one medium to another.

What establishes the frequency of an ultrasound wave? A. the transducer B. the medium through which the sound travels C. both A and B D. neither choice A nor B

A. When created by a transducer, an ultrasound wave has a specific frequency. the frequency is not determined by the medium through which the sound travels. Only the sound source ( the transducer) establishes the wave's frequency.

Which of the following units are appropriate to describe the period of an acoustic wave? (more than one answer may be correct.) A. minutes B. microseconds C. meters D. mm/micro sec E. cubic centimeters

A. and B. The period of a wave is defined as the time that elapse as a wave oscillates through a single cycle. The unit for period must be a measure of time, such as minutes or seconds. A and B are units of time.

Infrasound is defined as sound with a frequency of ______. A. greater than 20,000 kHz B. less than 20 Hz C. greater than 10 Mhz D. less than 0.02 MHz

B. Infra sound is defined as an acoustic wave with a frequency so low that it is not audible to humans. Infra sound is an inaudible wave with a frequency of less than 20 Hz

What term describes the number of cycles that an acoustic variavle completes in a second? A. period B. frequency C. pulse repetition period D. variable rate

B. frequency can also be thought of as the number of regularly occurring events in a specific time.

What is the range of period commonly found in waves produced by ultrasound systems? A. 0.001 to 1 s B. 0.06 to 0.5 micro sec C. 0.2 to 1 ms D. 10-100 ns

B. ultrasonic imaging waves have a period in range of 0.06 to 0.05 micro sec. The period is the time of a single cycle. Period is the reciprocal of frequency. A wave with a frequency of 2MHz has a period of 0.5 micro sec. A wave with a frequency of 15 MHz has a period of 0.06 micro sec.

With standard ultrasonic imaging, what happens to the period of a wave as it propagates? A. increases B. decreases C. remains the same

C. Certain parameters of a wave change as the wave travels through the body. However, the period and the frequency of a wave typically remains constant as a sound wave propagates.

When a sonographer increases the maximum imaging depth during an exam, what happens to the frequency? A. frequency increases B. frequency decreases C. remains unchanged

C. imaging depth and frequency are unrelated, when the depth of view is increased, the frequency of sound remains the same.

What is the range of frequencies emitted by transducers used in ultrasonic imaging? A. 1-3 MHz B. 1-1,000 kHz C. -10,000 to +10,000 Hz D. 2,000,000 to 15,000,000 Hz

D. Frequencies commonly used in diagnostic imaging range from approximately 2 to 15 megahertz or 2 to 15 million cycles per second.

Ultrasound is defined as a sound with a frequency of _____. A. greater than 20,000 kHz B. less than 1 kHz C. greater than 10 MHz D. greater than 0.02 MHz

D. Ultrasound is defined as ab acoustic wave a frequency so high that it is not audible to humans. Ultrasound us ab inaudible wave with a frequency of at least 20,000 Hz, 20 kHz or 0.02 MHz.

What is characteristic of acoustic waves with frequencies exceeding 20,000 Hz when compared with waves having frequencies of less than 20,000 Hz? A. they travel more effectively in soft tissue. B. they travel more rapidly C. the attenuate less when traveling in soft tissue D. humans cant hear them

D. Waves with frequencies exceeding 20 kHz are inaudible to humans and are called ultrasonic. They travel at the same speed as waves with lower frequencies and attenuate at a faster rate than waves with lower frequencies.

Which of the following cannot be considered a unit of frequency? A. per day B. cycles/sec C. Hz D. hertz E. cycles

E. The term cycles informs us of the number of events, but does not inform us of the duration of time required for those events to occur. Choice E is incomplete, and is not a unit of frequency. All the others choices reveal that a number of events took place in a specific time span.

True or false, The sonographer has the ability to alter the period of an ultrasound wave that is produced by a basic transducer.

False. The sonographer cannot adjust the period (or frequency) of a wave produced by a basic transducer. Think of sticking a key on a piano. The frequency of sound created by sticking a single key is constant. If the sound beam's frequency and period are not suited for the particular type of imaging, the sonographer must select a new transducer with a different frequency.

True or false, Waves in the ultrasound range behave in the same general manner as sound waves that are audible.

True. The primary difference between audible and ultrasonic waves is that humans can hear audible waves. A wave's behavior or adherence to physical laws and principals is generally the same, regardless of whether it can be heard by humans.