P3-Ultrasound and Total Internal Reflection

Question 1

Electrical systems can be made which produce electrical oscillations of any …………..
These can easily be converted into ………. vibrations to produce ……………….. ………..

Answer 1

Frequency
Mechanical
Ultrasound waves

Question 2

How does ultrasound imaging work?

Answer 2

When a wave passed from one medium to another-some of the wave is reflected and some is transmitted (partial reflection)
So a pulse of ultrasound is pointed at an object, and wherever there are boundaries, some waves get reflected back.
The time it takes for reflections to reach the detector can be used to measure how far away the boundary is.

Question 3

The time it takes for a reflected wave to reach the detector can be used to measure…..

Answer 3

How far away the boundary is

Question 4

The human ear can detect sound waves in the frequency range from around …….Hz to ……..Hz

Answer 4

20

20,000

Question 7

Ultrasound waves get …………… …………… at a boundary between media.

Answer 7

Partially reflected

Question 8

What is an ultrasonic (ultrasound) wave?

Answer 8

A sound wave above the frequency of a human ear

Question 11

Sound waves about the frequency of the human ear are called ……….. Waves

Answer 11

Ultrasonic (ultrasound)

Question 12

You can use ………………. ………….. to find boundaries

Answer 12

Oscilloscope traces

Question 13

What are the advantages of using ultrasonic waves instead of X Rays for medical scanning? Is that ultrasonic waves are…..(2)

Answer 13

• non ionising, therefore harmless

- reflected at boundaries between different types of tissues (unlike X Rays) so can be used to scan organs

Question 14

Name ways in which ultrasound can be used?

Answer 14

Breaking down kidney stones

Scanning fetus

Flaws in metal castings

Question 15

How do ultrasounds break down a kidney stone? Positives?

Answer 15

Concentrate high energy waves at the stone and turns it into sand-like particles.
Means patient doesn’t need surgery and is relatively painless

Question 16

What are ultrasound images usually like?

Answer 16

Fuzzy

Question 17

Light can be sent along ……….. …….. using total internal reflection

Answer 17

Optical fibres

Question 18

Total internal reflection can only happen when a wave travels through a ………. substance towards a ……….. substance.

Answer 18

Dense

Less dense

Question 19

If the angle of incidence is bigger than the critical angle…

Answer 19

No light comes out
It’s all internally reflected
(Total internal reflection)

Question 20

If the angle of incidence is equal to the critical angle ….

Answer 20

The emerging ray comes out along the surface. There’s quite a bit of internal reflection

Question 21

If the angle of incidence is less than the critical angle…

Answer 21

Most of the light passes out but a little bit is internally reflected

Question 22

The value of the critical angle depends of the ………….. ………

Answer 22

Refractive index

Question 23

A dense material with a high refractive index has a ……. critical angle

Answer 23

Low

Question 24

A medical use of optical fibres is…

Answer 24

Endoscopes