Doppler effect measure speed in blood cells

[hellokitty]

Homework Statement

A Doppler blood flow unit emits ultrasound at 5.0 {\rm MHz}.

What is the frequency shift of the ultrasound reflected from blood moving in an artery at a speed of 0.20 m/s?


What equations would I use to calculate the doppler shift? It is not in my textbook...

 

[Haths]

I believe off hand that the ratio of wavelenghts is equal to the ratio of speeds of the object;

L = wavelength
L₀ = wavelength before reflection
V = velocity of wave in medium
V₀ = velocity of wave.

V₀=fL₀ where f is the frequency of the ultrasound emitter.

L / L₀ = V / V₀

I think that's all the infomation required for the solution. See if you can do it now. If not highlight the below;



L / L₀ = 0.2 m/s / speed of sound ( 340 m/s) = Y

Where I'm just using Y to represent the ratio. The wave travels the same speed V in the medium of flesh (roughtly) hence;

Y = ( V/f ) / (V/f₀)

Rearrage for f;

1 / [(Y*( V / f₀ )) / V ] = f



However that might not be the question being asked or not, as you would require extra infomation to solve that numerically.

Haths

 

[hellokitty]

How do I solve for the wavelength if the wavelength is not given?