Chapter 16: Waves, Light Waves, Sound Waves, Ultrasound (the Physics of) Martin Caon Examination Questions and Answers in Basic Anatomy and Physiology Third Edition

Martin Caon Examination Questions and Answers in Basic Anatomy and Physiology Third Edition Chapter 16: Waves, Light Waves, Sound Waves, Ultrasound (the Physics of) 16.1 Waves Mechanical waves (sound waves, waves on water) are a mechanism for transferring energy through a medium (the air or water) without transferring matter. Another definition is: A periodic disturbance in some property of the medium, the medium itself remaining relatively at rest. Waves have the following measurable properties: 1. Wavelength (symbol λ) is the distance between two successive crests (in metres, m). A typical value is ~500 nm for light and ~20 cm for sound. 2. Frequency (f) is the number of λ that pass by in 1 s (in hertz, Hz). Typical values are 500 THz for light, 500 Hz for sound. Frequency is related to pitch (for sound) and colour (for visible light). 3. Period (T) is the time it takes for one λ to pass by (in seconds, s). 4. Speed (v) is how fast a wave is moving in the direction of propagation (in metres per second, m/s). The speed of light travelling through air is 3 × 108 m/s, while for sound, speed in air is about 330 m/s. In tissue, sound moves faster, at about 1560 m/s. 5. Amplitude (A) is the maximum displacement from the mean (or rest) position. For example the vertical distance between a trough and a crest of a wave in water is two times the amplitude. Amplitude (or intensity) is related to loudness of sound and brightness of light and to the amount of energy being carried by the wave. 6. Phase refers to how far out of step the oscillation of one part of a wave is when compared with another part. A phase of 0° or 360° means that the two parts are in step, while a phase difference of 180° means that the two points are completely out of step. Differences in phase between the sounds entering each ear allow us to localise the source of a sound. Some of these quantities are related to each other by the following formulae: v = fl; f = 1/T; E = h × f. 1. The amplitude of a wave is related to which of the following? a. The distance between two successive crests b. The number of wavelengths that pass by per second c. The speed of the wave’s travel d. The amount of energy it carries Answer is D: The greater the amplitude, the greater the energy carried. 2. Which is the BEST definition of a wave? a. The method by which the energy carried by visible light is propagated b. Travelling oscillations in the magnitude and direction of electric and mag-netic fields that do not require a material medium c. A periodic disturbance in some property of the medium, the medium itself remains (relatively) at rest d. A mechanism for the transfer of energy without the transfer of matter Answer is D: The other choices also describe a wave but not in the most general terms. 3. What does the term “wavelength” mean when applied to a wave? a. The number of complete cycles that pass by in 1 s b. The distance between two successive crests (or compressions) c. The time it takes for one wavelength to pass by d. How fast a wave is moving in its direction of propagation Answer is B: Wavelength is the shortest distance between two points that are displaying the same displacement. 4. The wave equation may be written in symbols as v = fλ where f stands for frequency, v stands for velocity and λ stands for wavelength. If a wave has a speed of 3 × 108 m/s, what is its frequency and wavelength? a. f = 10,000 Hz and λ = 0.0003 m b. f = 5 × 1014 Hz and λ = 6 × 10−7 m c. f = 6 × 104 Hz and λ = 0.5 × 10−4 m d. f = 2 MHz and λ = 3 × 105 m Answer is B: Which combination of frequency and wavelength will give the speed 3 × 108 m/s? v = fλ = 5 × 1014 Hz × 6 × 10−7 m = 30 × 1014–7 = 30 × 107 = 3 × 108. 5. The wave equation may be written in symbols as v = fλ where f stands for frequency, v stands for velocity and λ stands for wavelength. If a wave has a speed of 2 × 108 m/s, what is its frequency and wavelength? a. f = 4 × 104 Hz and λ = 0.5 × 10−4 m b. f = 5 × 1014 Hz and λ = 4 × 10−7 m c. f = 10,000 Hz and λ = 0.0002 m d. f = 2 MHz and λ = 1 × 105 m Answer is B: Which combination of frequency and wavelength will give the speed 2 × 108 m/s? v = fλ = 5 × 1014 Hz × 4 × 10−7 m = 20 × 1014–7 = 20 × 107 = 2 × 108. 6. What name is given to the change in the observed frequency of a wave (or its reflection) because of the motion of the source (or the reflecting object) or of the observer? a. Beat frequency b. Red shift c. Phase inversion d. Doppler effect Answer is D: The change in frequency when the source of the (say) sound is in motion relative to the observer is called the Doppler effect. (The red shift in astronomy is due to the Doppler effect.) 7. Which of the statements about sound and light is INCORRECT? a. Sound is a mechanical wave while light does not require a medium to travel in. b. Light is a transverse wave phenomenon while sound is a longitudinal wave phenomenon. c. The speed of light is much greater than the speed of sound. d. Ultrasound and ultraviolet light have frequencies less than infrasound and infrared light. Answer is D: In fact both ultrasound and ultraviolet light have frequencies GREATER than infrasound and infrared light respectively. 8. A wave may be defined as which of the following? a. The oscillation of a particle of the medium b. A series of crests and compressions that propagate through space c. A mechanism for the transfer of energy without transferring matter d. The transport of the medium due to the oscillation of its particles Answer is C: Essentially, a wave transfers energy without any matter moving away from its location. 9. Which of the following definitions of a wave is the best? a. A wave is an event or disturbance that is localised at a particular location. b. A mechanical wave is a periodic disturbance in a material medium. c. Waves are a means of transferring energy without transferring matter. d. Waves are a phenomenon characterised by their wavelength and their dis-placement of the medium from the mean position. Answer is C: This is the classic definition of a wave. Choices B and D are also true statements. 10. Which quantity most closely describes the amount of energy that is transported by a wave? a. Frequency b. Amplitude c. Wavelength d. Velocity Answer is B: Energy and amplitude are directly related.