1. Dec 27, 2007

### DEWANA

Hi guys I hope U can help me with this calculation....

Im very bad in Physics....I have no Idea how to caluculate this equation
And I dont no how to start...please helppp mee........It help me very much to see how you calculate it THANK YOU VERY MUCH:

It says:
Use the data from the table below to calculate the specific acousstic impedance, Z of
i) air, ii) skin, iii) fat. Use the equation Z = pc

Medium Densit (p) kg m-3 Ultrasound velocity (c) m s-1
air 1.3 330
skin 1060 1540
fat 925 1450

Using the following equation:

α = (Z2 - Z1)
(Z2 + Z1)

caluculate the intensity reflection coefficient, α at iv) an air-skin boundry, v) a skin-fat boundry. Show all stages of your working.

2. Dec 27, 2007

### DEWANA

Thank U so much

3. Dec 27, 2007

### arildno

It says:
Use the data from the table below to calculate the specific acousstic impedance, Z of
i) air, ii) skin, iii) fat. Use the equation Z = pc

Medium Densit (p) kg m-3 Ultrasound velocity (c) m s-1
air 1.3 330
skin 1060 1540
fat 925 1450

Are you seriously saying you are unable to calculate Z=pc in these three cases???

4. Dec 27, 2007

### DEWANA

thanks

maria )

5. Dec 27, 2007

### arildno

What does "Z" stand for?
What does "p" stand for?
What does "c" stand for?

6. Dec 27, 2007

### dynamicsolo

Is this issue here that you don't understand what is meant by 'pc'? For this part, they are just asking you to multiply together the values given in the table for each substance.

For this second part, you would use the appropriate values of Z that you found in the first part to calculate $$\alpha$$ for each possible pair of substances. (Arrange the values in the numerator so that the difference is always positive.)

You are welcome to show the results you found if you have any questions about whether they are correct...

7. Dec 28, 2007

### TVP45

DEWANA,
I ask this in what I hope you take as helpful. Do you know the physical meaning of what you are calculating? This reflection coefficient tells you what happens when a sound wave travelling in one medium (like water) hits the boundary between that medium and another medium (say air, or rock, or steel). If you have further interest, you might look up how sonar works and how the waves are reflected from the boundary between seawater and a steel hull. It tells you how a sonar operator knows the difference between a whale and a Red October or why hulls are sometimes coated with a substance similar to rubber. Sonar is not nearly the only application, but it might be interesting to see what the calculation means.