P3 1 - Medical applications of physics

Question 1

Properties of x-rays

Answer 1

Affect a photographic film similar to light
Can be absorbed by metal and bone
Are transmitted by healthy tissue

Question 2

Why do CT scanners use x-rays?

Answer 2

CT scanners use x-rays to produce digital images of a cross-section through the body.

Question 3

Why are x-rays dangerous?

Answer 3

X-rays cause ionisation and can damage living tissue when they pass through it.

Question 4

Range of hearing for a human ear

Answer 4

20Hz-20kHz

Question 5

How can a ultrasound wave give us an indication on how far away an object is?

Answer 5

When a wave meets a boundary between 2 different materials, part of the wave is reflected and travels back to a detector. The time it takes to reach the detector can be used to calculate how far away the boundary.

Question 6

Equation for distance

Answer 6

Distance = speed x time

Question 7

Advantages of using ultrasound instead of x-rays

Answer 7

Non-ionising - safer to use

Question 8

Uses of ultrasound

Answer 8

Scanning unborn babies and soft tissue (e.g. The eye)

Shattering kidney stones

Question 9

What is refraction?

Answer 9

The change of direction of light as it passes from one substance into another

Question 10

Why does refraction occur?

Answer 10

Waves change speed when they cross a boundary. The change in speed of the waves causes a change in direction, unless the wave is travelling along a normal.

Question 11

Equation for the refractive index

Answer 11

Sin (the angle of incidence) ÷ sin (the angle of refraction)

Question 12

What is the critical angle?

Answer 12

The angle of incidence of a light Ray in a transparent substance which produces refraction along a boundary.

Question 13

What happens when the angle of incidence increases beyond the critical angle?

Answer 13

Mum’s favourite thing about physics!

Angle of reflection = angle of incidence

Question 14

Equation for the refractive index

Answer 14

1 ÷ sin (critical angle)

Question 15

Range of hearing for a human ear

Answer 15

20Hz-20kHz

Question 16

How can a ultrasound wave give us an indication on how far away an object is?

Answer 16

When a wave meets a boundary between 2 different materials, part of the wave is reflected and travels back to a detector. The time it takes to reach the detector can be used to calculate how far away the boundary.

Question 17

Equation for distance

Answer 17

Distance = speed x time

Question 18

Advantages of using ultrasound instead of x-rays

Answer 18

Non-ionising - safer to use

Question 19

Uses of ultrasound

Answer 19

Scanning unborn babies and soft tissue (e.g. The eye)

Diagnosis and shattering of kidney stones

Question 20

What is refraction?

Answer 20

The change of direction of light as it passes from one substance into another

Question 21

Why does refraction occur?

Answer 21

Waves change speed when they cross a boundary. The change in speed of the waves causes a change in direction, unless the wave is travelling along a normal.

Question 22

Equation for the refractive index

Answer 22

Sin (the angle of incidence) ÷ sin (the angle of refraction)

Question 23

What is the critical angle?

Answer 23

The angle of incidence of a light ray in a transparent substance which produces refraction along a boundary.

Question 24

What happens when the angle of incidence increases beyond the critical angle?

Answer 24

Mum’s favourite thing about physics!

Angle of reflection = angle of incidence

Question 25

Equation for the refractive index

Answer 25

1 ÷ sin (critical angle)

Question 26

What are the uses of x-rays?

Answer 26

They make images and CT scans
They destroy tumours at/near the body-surface
They are also used to challenge GCSE physics students

Question 27

What is the refractive index of a substance?

Answer 27

It is a measure of how much the substance can reflect a light ray.

Question 28

What is an endoscope?

Answer 28

It is a device to look inside a patient’s body without cutting it open or to perform keyhole surgery. It contains bundles of optic fibres. Visible light can be sent along the fibres by total internal reflection.

Question 29

When will I, will I be famous?

Answer 29

I can’t answer, I can’t answer that

Question 30

What is an optical fibre?

Answer 30

Very thin flexible glass tubes

Question 31

What does a converging lens do?

Answer 31

It focuses parallel rays to a point called the principal focus. There is a principal focus on each side of the lens.

Question 32

What is the focal length?

Answer 32

The focal length is the distance from the centre of the lens to the principal focus.

Question 33

When is a real image formed by converging lens.

Answer 33

An inverted real image is formed if the object is further away than the principal focus. The nearer the object to the lens, the larger the image.

Question 34

When is a virtual image formed by a converging lens?

Answer 34

If an object is nearer to the lens then the punk of thinkable focus and, and upright, virtual image is formed behind the object. Is the image is the magnified.

Question 35

How do we calculate magnification?

Answer 35

Image height / object height

Question 36

What happens to parallel rays of light that pass through a diverging lens?

Answer 36

They are refracted so that they diverge away from the principle focus

Question 37

What type of image is produced by a diverging lens?

Answer 37

A virtual image