IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: vanibharutham on March 15, 2010, 01:28:28 pm

Title: Physics - Ultrasound Doubt
Post by: vanibharutham on March 15, 2010, 01:28:28 pm

An ultrasound system for examining an eye sends out a pulse of ultrasound waves with a frequency of 6 MHz. The pulse duration is 0.6microseconds. The speed of sound in the body is approximately 1510 m/s.
What is the resolution of image produced?

The book calculates two answers:

1) 0.453 mm
2) 0.251 mm

It then says for these two results we take the larger, worse resolution. Finer details than this could not be seen in the image produced.

Could someone please explain how to get the resolution using the pulse-length method and what resolution is?

Title: Re: Physics - Ultrasound Doubt
Post by: Saladin on March 15, 2010, 01:56:47 pm

Your first answer is wrong, but your second answer is right. The worked examples are attatched.

Hope you find them useful.

Cheers.

Title: Re: Physics - Ultrasound Doubt
Post by: astarmathsandphysics on March 15, 2010, 02:09:02 pm

wavelength=speed/frequency=1510/6000000=0.252mm

resolution=pulse length/2=(1510*0.6*10^-6)/2=0.453mm

Title: Re: Physics - Ultrasound Doubt
Post by: Saladin on March 15, 2010, 02:12:21 pm

oops 4got to half....

its not fair how u always get it right.

Title: Re: Physics - Ultrasound Doubt
Post by: astarmathsandphysics on March 15, 2010, 03:24:56 pm

It was other way round earlier. You gov one right and I gov it wrong

Title: Re: Physics - Ultrasound Doubt
Post by: vanibharutham on March 15, 2010, 05:16:57 pm

cheers guys :)

any reason why u have to half the pulse length?

Title: Re: Physics - Ultrasound Doubt
Post by: astarmathsandphysics on March 15, 2010, 06:43:47 pm

inteference between the pulse ends