1.14 Ultrasound

Question 1

What is ultrasound?

Answer 1

Sound that vibrates at frequencies above 20,000 Hz

Question 2

Why do bats naturally produce ultrasound? (2)

Answer 2

• Communication
• Echo location

Question 3

How is ultrasound made?

Answer 3

Electrical devices can be made which produce electrical oscillations of any frequency. These can easily be converted into mechanical vibrations to produce sound waves beyond 20,000 Hz.

Question 4

Describe how sound waves get partially reflected at boundaries

Answer 4

When a sound wave passes from one medium into another, some of the wave is reflected off the boundary between the two media, and some is transmitted (and refracted). This is partial reflection.

Question 5

How is ultra sound used in medical imaging? (2)

Answer 5

• Ultrasound waves can pass through the body, but whenever they reach a boundary between two different media (like fluid in the womb and the skin of the foetus) some of the wave is reflected back and detected.
• The exact timing and distribution of these echoes are processed by a computer to produce a video image of the foetus.

Question 6

How is ultrasound used in industrial imaging? (2)

Answer 6

Ultrasound can be used to find flaws in objects such as pipes or materials such as wood or metal.
- Ultrasound waves entering a material will usually be reflected by the far side of the material.
- If there is a flaw such as a crack inside the object, the wave will be reflected sooner.

Question 7

How can ultrasound be used in echo sounding?

Answer 7

Boats and submarines will fire ultrasounds at the sea floor or other objects in the ocean to find how far away they are.