Unformatted text preview: PHY2054 Spring 2008 14. (J'mta. 2.124) As shown in the ﬁgure, a narrow beam of ultrasonic waves enters the liver at /\ an angle 9= 50°, reﬂects offa tumor inside the liver and its outgoing direction and location are A 1 / D" "W
measured. If the speed of the wave isJJl‘Lless in the liyet,t,h§n._i_n the surroundingtissue, determine the depth d of the tumor (in cm). Assume that A = 12 cm. @59 (2) 5.0
(3) 7.8
(4) 7.3
(5) None of these The displacement A is given ﬁ'om geometry by A = 2d tan 02 , where 0; is the refracted angle
whose size is given by Snell’s law (using nﬁm / nﬁm = l/ 0.93 = 1.075). This give 02 = 45 .4° .
Solving for d yields d = 5. 9 cm. 15. (fmiv, 22. 25) TWO identical light pulses are emitted simultaneously from a laser (it = 632.8
nm ). The pulses immediately enter two different media and take parallel paths to a detector 5.90
m away, one passing through air and the other through a block of ice (n = 1.31. Determine the
difference in the Bulges nﬂs of arrival (in nsec) at the detector. @61 (2) 19.7 (3) 4.7 (4) 15.0 (5) None of these Ihetimedmiemncea=tztlisgivenby At=L/(c/n2)~L/(c/n,)=l.(n2—n,)/c. Usingthe
valuesL = 5.9, n; = 1.31, n; = 1.0, we obtain 1 = 6.1 nsec. 16. Refer to the previous problem. Over WW (in pm) will the W5
{weed by the WWW 7? @143
4.4 (3) 5.8
(4) 1.50
(5) 3.4 Let the common distance traveled by called d. Then the diﬂizrence in the number of waves
traveledin each medium is AN =d/(zl/n2)d/(zi./n1) =(n2 n,)d/A . Using ,1 = 632.8 nm, AN = 7 and the values of n; and n; from the previous problem, we obtain d = 14.3 m. ...
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 Spring '09
 DUNNAM

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