Answer:
b. 0.75 mm
Explanation:
The distance between antinodes d is half the wavelength [tex]\lambda[/tex]. We can obtain the wavelength with the formula [tex]v=\lambda f[/tex], where f is the frequency given ([tex]f=1MHz=1\times10^6Hz[/tex]) and v is the speed of sound in body tissues (v=1540m/s), so putting all together we have:
[tex]d=\frac{\lambda}{2}=\frac{v}{2f}=\frac{1540m/s}{2(1\times10^6Hz)}=0.00077m=0.77mm[/tex]
which is very close to the 0.75mm option.