66 MATTER WAVES: SOUND AND ULTRASOUND 



PROBLEMS 



3- 1 : Express in decibels the sound which delivers 1 50 times the power of background 



noise. 

 3-2: (a) Calculate the value of the absorption coefficient of sound in tissue at 50; 

 1000; 10,000; and 500,000 cycles per second (cps). 



(b) Make a plot of intensity vs depth in tissue for each frequency. 

 3-3: How would you employ the inverse square law to "protect" yourself from an 



intense source of noise? Suppose you wanted to reduce the noise level by 



a factor often. 



What could you learn about this problem from a = f(rj) as these terms are 



defined in the text? 

 3-4: Two signals enter your ear: one at 500 cps, with intensities / and 7° equal to 



10~ I2 and 10" l5 w/cm 2 , respectively; and the other at 6000 cps with intensities 



/and 1° equal to 10 14 and 10~ 16 w/cm 2 . Which will seem the louder? 



REFERENCES 



1. Fry, W. J., Adv. in Biol, and Med. Phys., 6,281 (1959): a review, illustrated. 



2. Kelly, E., Ed., "Ultrasound in Biology and Medicine," Amer. Inst, of Biol. Sciences, 



Washington, D. C, 1957. 



3. Fletcher, H., "Speech and Hearing," D. Van Nostrand Co., Inc., New York, 



N.Y., 1946. 



4. Ruch, T. C. and Fulton, J. F., Eds., "Medical Physiology and Biophysics," 



W. B. Saunders Co., Philadelphia, Pa., 1960. 



5. Herzfeld, K. F. and Litovitz, T. A., "Absorption and Dispersion of Ultrasonic 



Waves," Academic Press, New York, N. Y., 1959. 



6. Stacy, R. W., Williams, D. T., Worden, R. E., and McMorris, R. O., "Essen- 



tials of Biological and Medical Physics," McGraw-Hill Book Co., Inc., New 

 York, N. Y., 1955. 



7. Whitfield, I. C, "The Physiology of Hearing," in Progr. in Biophysics, 8, 1 (1957); 



a review. 



8. Gray, J. A. B., "Mechanical into Electrical Energy in Certain Mechano- 



Receptors," Progr. in Biophysics, 9, 285 (1959); a review. 



9. Neely, K. K., "Noise — Some Implications for Aviation," Can. Aeronaut. J., 3, 



312(1957). 



10. Herrick,J. F. and Anderson, J. A., "Circulatory System: Methods — Ultrasonic 



Flow Meter," in "Medical Physics," Vol. Ill, O. Glasser, Ed., Yearbook 

 Publ., Inc., Chicago, 111., 1960, p. 181. 



11. Gardner, W. H., "Speech Pathology," ibid., p. 637. 



12. Herrick, J. F., Proc. Inst. Radio Engineers, Nov., 1959, p. 1957. 



13. Von Bekesy, G., "The Ear,"5W. Amer., Aug., 1957; a review. 



