1. Peer Mark Wave Equation Practice
2 x 10 = 20 m/s
0.01 x 400 = 4 m/s
5/1 = 5 m
330/40 x 103 = m
330/30 x 10-3 = 33.3 Hz

2. Peer Mark Wave Equation Practice
Lowest note = 330/20 = 16.5 m
Highest note = 330/ 20 x 103 = 0.02 m
T = 5 seconds f = 1/T = 0.2 Hz
v = 0.2 x 15 = 3 m/s
x 108 / 200 x 103 = 1500 m

3. Learning Objectives
By the end of this lesson you should be able to…
Define ultrasound
Explain how ultrasound can be used to detect and explore surfaces / objects that can’t be seen.
Explain how ultrasound can be used in echo sounding and in medical imaging.

4. Ultrasound Any sound above the highest frequency humans can hear
(f > 22 kHz).
Increasing frequency (Hz)
Ultrasound
Above 20,000Hz
Audible sound
2 – 20,000 Hz
Earthquake waves
Below 2 Hz

5. Uses of Ultrasound?

6. Less Obvious Uses of Sounds
Boats and submarines use echo sounding, or sonar. This can tell the sailors how deep the water is or whether there are other objects, such as mines, submarines, or fish beneath them. How so?

7. Example
A boat sends out a sonar 'ping' straight down into the sea, four seconds later the echo is detected. How deep is the water?
[The speed of sound in water is 1500 m/s.]

8. Uses of Ultrasound Baby scanning
Sound reflects off of hard surfaces – bone, cartilage, organs.
This allows us to ‘see’ unborn babies and check their development.
The sound used for this is very high frequency – about
Hz.

9. Ultrasound: Ultrasonic scanner
The time taken for these reflections can be used to measure the depth of the reflecting surface and this information is used to build up a picture of the object being examined.
Ultrasonic waves are partly reflected at the boundary as they pass from one medium to another.
1MHz

10. Note speed of sound in water (or amniotic fluid) is 1497m/s.
A pulse of ultrasound is sent into a pregnant mothers womb. The reflection off the left side of the foetuses head is received 1.07x10-4 seconds later. The reflection off the right side of the foetuses head is received 2.40x10-4 after being sent. How wide is the baby’s head?
Note speed of sound in water (or amniotic fluid) is 1497m/s.
Take care with distance of journey.

11. 3D Ultrasounds – New Tech!
Ultrasound Images – Week by Week

12. Why not X ray the baby?
X-rays are known to be dangerous as they are ionising.
X-rays constitute a dangerous form of radiation and whilst in an adult the benefits might outweigh the risks it is not reasonable to subject the baby to them.
ALARA Principle
Ultrasound is believed to be totally safe.

13. Why not X ray the baby?

14. Treating Kidney stones
Extracorporeal shock wave lithotripsy!
Surgery very painful.
Ultrasound can vibrate the stone until it shatters.
This is a bit like an opera singer breaking a wine glass!
The kidney stone can then be passed out of the body.

15. Questions
Have a go at answering these questions

16. X-Ray, Gamma or Ultrasound?
6. Causes compressions and rarefactions as it travels
EM Wave
2. Longitudinal Wave
7. No effect on living tissue
3. Ionising
8. Produced by firing electrons at metals
4. Produced by the nuclei of radioactive atoms
9. Absorbed only by thick lead
5. Absorbed by bone

17. Homework
Answer all questions from the sheet.