==Medical Physics== What are rayls? (1 Viewer)

[tt_j65]

We are in class right now and we are stuck in what are rayls (referring to acoustic impedance)

What are the units for Rayls?

there are several answers from different text books such as kgm^-2s^-1 or kgm^-2

thanks

 

[Insomniac]

Originally posted by tt_j65
We are in class right now and we are stuck in what are rayls (referring to acoustic impedance)

What are the units for Rayls?

there are several answers from different text books such as kgm^-2s^-1 or kgm^-2

thanks

first one i think ...
acoustic impedance has velocity in it, so there should be s^-1

 

[wogboy]

The acoustic impedance (Z) is defined as:

Z = pv

(p = density, v = speed of sound in that medium)

Because p has the SI units kg/m<SUP>3</SUP>, and v has the SI units m/s, then Z has the SI units of measurement kg/(m<SUP>2</SUP>s). i.e. kilograms per metres squared per second.

Because this unit of measurement kg/(m<SUP>2</SUP>s) is a pain the arse to write , it's simply called a Rayl.

1 Rayl = 1 kg/(m<SUP>2</SUP>s)

 

[wogboy]

Also, the unit of measurement Rayl is too small to be commonly used. You might see it written as MRayl (megarayl) which just means 10^6 rayls (a million rayls) e.g. To find the acoustic impedance for water:

p(water) = 1 g/cm^3 = 1000 Kg/m^3
v(water) = 1500 m/s

so Z(water) = 1500000 Rayls = 1.5 MRayls