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Section
III
Questions 13 - 17:
Question 13
B We are
told the value is obtained by multiplying the density of material by the speed
of sound in the material. The units of density are kgm-3 and of speed are ms-1.
So multiplying these gives the answer B
Question 14
C The
values of the two media have the greatest difference.
Question 15
C The actual calculation is  = (1.7 x 106 - 1.59 x 106)2 / (1.7 x 106
+ 1.59 x 106)2 = 1.21 x1010 / 1.0824 x 1013
Question 16
D
For the value to be close to 1 we require a large difference in the acoustic
impedances of the two materials. The greatest difference is between blood and
bone.
Question 17
A We know the speed is 1500ms-1. In this
time 2 x 106 waves pass. Hence frequency = 1500 / 2 x 106 = 7.5 x 10-4 m; or
0.75mm
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