I need help

I was wondering if someone could help me. How i can calculate diameter of baby head if there is time delay of 96 microseconds between receiving pulses from either side of the skull , and the speed of the ultrasounds is 1250 m/s?
Thank you

Reply 1

squidge_gt

How much further has the sound wave to the opposite side of the head travelled than the one to the near side? If you know this, then you can use this, the time delay and the speed of sound to calculate the diameter

Reply 2

Dani69

Original post by squidge_gt

Thank you but these are all details that I have in the question-do I have to multiply the values i was given?

Reply 3

Stonebridge

Original post by Dani69

Thank you but these are all details that I have in the question-do I have to multiply the values i was given?

Distance = speed x time

so yes.

Just make sure that you remember that a microsecond is 10^-6 seconds.

(edited 2 years ago)

Reply 4

Dani69

Original post by Stonebridge

Distance = speed x time

so yes.

Just make sure that you remember that a microsecond is 10^-6 seconds.

Thank you so much indeed.

Reply 5

squidge_gt

Original post by Dani69

Thank you so much indeed.

Just remember to consider the fact that this distance is the extra distance recalled by the sound wave going to the other side of the head, so it isn’t the diameter of the baby’s head, you have to calculate the diameter from this distance

Reply 6

Dani69

I am getting a bit confused now...Do I have to divide 96 microseconds by 2 ?

Reply 7

ThiagoBrigido

Original post by Dani69

I am getting a bit confused now...Do I have to divide 96 microseconds by 2 ?

Post #4 already gave you the answer. What is the diameter? What are you trying to find?

Reply 8

Dani69

Original post by ThiagoBrigido

Post #4 already gave you the answer. What is the diameter? What are you trying to find?

Trying to find diameter of baby head with these values i was given

Reply 9

Stonebridge

Original post by Dani69

Trying to find diameter of baby head with these values i was given

I think the wording of the question is a little confusing.
What do they mean by 'delay' here?

It seems like they are saying that it takes 96 microseconds for the sound to pass through the head at the given speed.
I wouldn't call that a 'delay' exactly, more an 'interval'.
If this is what they mean then you just multiply the 2 values given as I said.

The other meaning of 'delay' would require a different calculation where you would need to be given the speed of the sound waves in air and compare the time taken for the sound to travel through the head with the time taken to travel through thin air.
In this case the sound through the head would arrive earlier that the thin air sound as it travels faster through a solid - in this case the head.
So in effect there would not be a 'delay'. At least not the sound wave we are talking about.

With just the information given in this question, the 1st interpretation seems logical.

So my original reply is still the best bet. :wink:

Reply 10

squidge_gt

Original post by Stonebridge

I think The delay comes from the fact that the sound waves are reflecting off of the head, some off of the near side and some off the side further away from the detector, so the ones going to the near side just travel from the detector to the near side of the head and back again, whereas the ones going to the far side go through to the other side of the head and are reflected at the head- air boundary, so they travel an extra distance by going across the baby’s head twice, once on the way there, and once on the way back. This extra distance travelled accounts for the time delay between when the detector receives the pulses.